to-words

Convert numbers and currency amounts into words across 136 locales — production-ready BigInt, ordinal, and TypeScript support.

import { toWords } from 'to-words';

toWords(12345, { localeCode: 'en-US' });
// "Twelve Thousand Three Hundred Forty Five"

toWords(452.36, { localeCode: 'en-IN', currency: true });
// "Four Hundred Fifty Two Rupees And Thirty Six Paise Only"

Try the interactive demo → — currency, ordinals, gender, and large numbers, live in the browser.

Need the reverse conversion too? Use the companion package to-numbers to parse spelled-out numbers back into numeric values across the same locales.

📑 Table of Contents

• Use Cases
• Features
• Quick Start
• Installation
• Usage
• Migration Guide
• CLI
• Framework Integration
• Numbering Systems
• API Reference
  • Constructor Options
  • Class Methods
  • Functional Exports
  • Converter Options
• Spelled-Out Decimal (Fraction Style)
• Bundle Sizes
• Performance
• Browser Compatibility
• Supported Locales
• Error Handling
• Support
• Contributing
• FAQ
• Changelog
• License

💼 Use Cases

• Invoicing & Billing — Display amounts in words on invoices, receipts, and financial documents
• Check Printing — Banks and financial institutions require amounts in words for check validation; use decimalStyle: 'fraction' for legal positional notation ("Forty-Five Hundredths")
• E-commerce — Show order totals in words for clarity and accessibility
• Legal Documents — Contracts and agreements often require written-out amounts, including spelled-out decimals
• Educational Apps — Teach number pronunciation and spelling in different languages
• Accessibility — Screen readers benefit from properly formatted number-to-text conversion
• Localization — Support global users with region-specific number formatting

✨ Features

• 136 Locales — The most comprehensive locale coverage available
• BigInt Support — Exact integer input beyond Number.MAX_SAFE_INTEGER, with locale-specific supported ranges
• Multiple Numbering Systems — Short scale, Long scale, Indian, and East Asian
• Currency Formatting — Locale-specific currency with fractional units
• Ordinal Numbers — First, Second, Third, etc.
• Gender-Aware — Grammatical gender for locales that require it (Spanish, Portuguese, Arabic, Hebrew, Slavic, and more)
• Fraction-Style Decimals — Legal/financial positional decimals ("Forty-Five Hundredths") via decimalStyle: 'fraction' across 100 locales
• Formal Numerals — Formal/financial Chinese characters (大写/大寫) via formal: true
• Tree-Shakeable — Import only the locales you need
• TypeScript Native — Full type definitions included
• Multiple Formats — ESM, CommonJS, and UMD browser bundles
• Zero Dependencies — Lightweight and self-contained
• High Performance — Up to 4.7M ops/sec (small integers; see benchmark section for full breakdown)
• Functional API — toWords(), toOrdinal(), toCurrency() named exports for ergonomic one-liners
• Auto Locale Detection — detectLocale() reads navigator.language or Intl in any runtime
• Typed Locale Resolution — Generated LocaleCode union plus resolveLocale() for dynamic BCP 47 input
• Strict Locale Ranges — Form-specific ceilings with structured errors and explicit legacy composition mode
• Capability Manifest — Query supported locales and derived feature support through to-words/manifest
• CLI — npx to-words 12345 --locale en-US for shell scripts and quick conversions
• Wide Compatibility — All modern browsers and Node.js 20+; compatible by architecture with Deno, Bun, and Cloudflare Workers (zero Node.js-specific APIs)

🚀 Quick Start

There are three ways to use to-words. Pick the one that fits your use case:

1. Class-based — best for high-volume workloads where you reuse one instance:

import { ToWords } from 'to-words';

const tw = new ToWords({ localeCode: 'en-US' });
tw.convert(12345); // "Twelve Thousand Three Hundred Forty Five"
tw.convert(100, { currency: true }); // "One Hundred Dollars Only"
tw.toOrdinal(3); // "Third"

2. Functional (full bundle) — one-liners with a localeCode option, all 136 locales available:

import { toWords, toOrdinal, toCurrency } from 'to-words';

toWords(12345, { localeCode: 'en-US' }); // "Twelve Thousand Three Hundred Forty Five"
toCurrency(100, { localeCode: 'en-US' }); // "One Hundred Dollars Only"
toOrdinal(3, { localeCode: 'en-US' }); // "Third"

3. Functional (per-locale import) — locale baked in, fully tree-shakeable, smallest bundle:

import { toWords, toOrdinal, toCurrency } from 'to-words/en-US';

toWords(12345); // "Twelve Thousand Three Hundred Forty Five"
toCurrency(100); // "One Hundred Dollars Only"
toOrdinal(3); // "Third"

Default locale: When no localeCode is provided, the runtime locale is auto-detected via detectLocale() and falls back to en-IN if it cannot be matched.

📦 Installation

Runtime requirement: Node.js >= 20.

Moving from another library? See MIGRATION.md.

npm / yarn / pnpm

npm install to-words
# or
yarn add to-words
# or
pnpm add to-words

CDN (Browser)

<!-- Full bundle with all locales -->
<script src="https://cdn.jsdelivr.net/npm/to-words/dist/umd/to-words.min.js"></script>

<!-- Single locale bundle (smaller, recommended) -->
<script src="https://cdn.jsdelivr.net/npm/to-words/dist/umd/en-US.min.js"></script>

📖 Usage

Importing

// Class-based — ESM
import { ToWords } from 'to-words';

// Class-based — CommonJS
const { ToWords } = require('to-words');

// Functional helpers (full bundle) — ESM
import { toWords, toOrdinal, toCurrency, detectLocale } from 'to-words';

// Functional helpers (per-locale, tree-shakeable) — ESM
import { toWords, toOrdinal, toCurrency } from 'to-words/en-US';

// Per-locale class — ESM
import { ToWords } from 'to-words/en-US';

Basic Conversion

Class-based:

const tw = new ToWords({ localeCode: 'en-US' });

tw.convert(123); // "One Hundred Twenty Three"
tw.convert(123.45); // "One Hundred Twenty Three Point Four Five"
tw.convert(123.045); // "One Hundred Twenty Three Point Zero Four Five"

Functional (full bundle):

import { toWords } from 'to-words';

toWords(123, { localeCode: 'en-US' }); // "One Hundred Twenty Three"
toWords(123.45, { localeCode: 'en-US' }); // "One Hundred Twenty Three Point Four Five"

Functional (per-locale):

import { toWords } from 'to-words/en-US';

toWords(123); // "One Hundred Twenty Three"
toWords(123.45); // "One Hundred Twenty Three Point Four Five"

Note: When the fractional part starts with zero, digits after the decimal point are converted individually. For legal/financial positional notation ("Forty-Five Hundredths"), see decimalStyle: 'fraction'.

BigInt & Large Numbers

Handle numbers beyond JavaScript's safe integer limit without precision loss. Strict mode accepts values through the active locale's published ceiling:

const toWords = new ToWords({ localeCode: 'en-US' });

// Using BigInt
toWords.convert(1000000000000000000n);
// "One Quintillion"

toWords.convert(1000000000000000000000000000000000000000000000000000000000000000n);
// "One Vigintillion"

// Using string for precision
toWords.convert('9007199254740993');
// "Nine Quadrillion Seven Trillion One Hundred Ninety Nine Billion
//  Two Hundred Fifty Four Million Seven Hundred Forty Thousand Nine Hundred Ninety Three"

// Legacy recursive scale composition is still available explicitly
toWords.convert('1e100', { rangeMode: 'compose' });

Currency Conversion

Class-based:

const tw = new ToWords({ localeCode: 'en-IN' });

tw.convert(452, { currency: true });
// "Four Hundred Fifty Two Rupees Only"

tw.convert(452.36, { currency: true });
// "Four Hundred Fifty Two Rupees And Thirty Six Paise Only"

// Without "Only" suffix
tw.convert(452, { currency: true, doNotAddOnly: true });
// "Four Hundred Fifty Two Rupees"

// Ignore decimal/fractional part
tw.convert(452.36, { currency: true, ignoreDecimal: true });
// "Four Hundred Fifty Two Rupees Only"

// Ignore zero currency
tw.convert(0.36, { currency: true, ignoreZeroCurrency: true });
// "Thirty Six Paise Only"

// Show fractional unit even when zero (string input preserves .00)
tw.convert('452.00', { currency: true, includeZeroFractional: true });
// "Four Hundred Fifty Two Rupees And Zero Paise Only"

Functional — toCurrency() shorthand:

import { toCurrency } from 'to-words';

toCurrency(452, { localeCode: 'en-IN' });
// "Four Hundred Fifty Two Rupees Only"

toCurrency(452.36, { localeCode: 'en-IN' });
// "Four Hundred Fifty Two Rupees And Thirty Six Paise Only"

toCurrency(452, { localeCode: 'en-IN', doNotAddOnly: true });
// "Four Hundred Fifty Two Rupees"

Functional per-locale (locale baked in, no localeCode needed):

import { toCurrency } from 'to-words/en-IN';

toCurrency(452); // "Four Hundred Fifty Two Rupees Only"
toCurrency(452.36); // "Four Hundred Fifty Two Rupees And Thirty Six Paise Only"

Custom Currency

Override currency settings while keeping the locale's language:

const toWords = new ToWords({
  localeCode: 'en-US',
  converterOptions: {
    currency: true,
    currencyOptions: {
      name: 'Euro',
      plural: 'Euros',
      symbol: '€',
      fractionalUnit: {
        name: 'Cent',
        plural: 'Cents',
        symbol: '',
      },
    },
  },
});

toWords.convert(100.5);
// "One Hundred Euros And Fifty Cents Only"

3-Decimal Currencies

Currencies like OMR (Omani Rial), IQD (Iraqi Dinar), KWD (Kuwaiti Dinar), and BHD (Bahraini Dinar) use 1000 minor units per major unit (3 decimal places). The en-OM, en-IQ, and ar-IQ locales have precision: 3 built in:

const toWords = new ToWords({ localeCode: 'en-OM' });

toWords.convert('500.500', { currency: true });
// "Five Hundred Omani Rials And Five Hundred Baisa Only"

toWords.convert('2.010', { currency: true });
// "Two Omani Rials And Ten Baisa Only"

toWords.convert('2.100', { currency: true });
// "Two Omani Rials And One Hundred Baisa Only"

For a custom 3-decimal currency, pass precision: 3 in currencyOptions:

const toWords = new ToWords({ localeCode: 'en-US' });

toWords.convert('1.500', {
  currency: true,
  currencyOptions: {
    name: 'Kuwaiti Dinar',
    plural: 'Kuwaiti Dinars',
    symbol: 'KWD',
    precision: 3,
    fractionalUnit: { name: 'Fils', plural: 'Fils', symbol: '' },
  },
});
// "One Kuwaiti Dinar And Five Hundred Fils Only"

Note: JavaScript number literals cannot express trailing zeros (500.500 === 500.5 in JS). For 3-decimal currencies, always pass the value as a string ('500.500') to preserve the intended precision.

Ordinal Numbers

Class-based:

const tw = new ToWords({ localeCode: 'en-US' });

tw.toOrdinal(1); // "First"
tw.toOrdinal(21); // "Twenty First"
tw.toOrdinal(100); // "One Hundredth"

Functional — toOrdinal() (full bundle):

import { toOrdinal } from 'to-words';

toOrdinal(1, { localeCode: 'en-US' }); // "First"
toOrdinal(21, { localeCode: 'en-US' }); // "Twenty First"
toOrdinal(100, { localeCode: 'en-US' }); // "One Hundredth"

Functional per-locale:

import { toOrdinal } from 'to-words/en-US';

toOrdinal(1); // "First"
toOrdinal(21); // "Twenty First"

Note: Full ordinal word mappings are available for English, Spanish, French, Portuguese, Turkish, and Dutch locales. Other locales use locale-specific suffix or prefix strategies.

Gender-Aware Conversion

Many languages use grammatical gender for number words. Pass gender via converter options:

// Spanish: masculine (default) vs feminine
const tw = new ToWords({ localeCode: 'es-ES' });
tw.convert(1); // "Uno"
tw.convert(1, { gender: 'feminine' }); // "Una"
tw.convert(21, { gender: 'feminine' }); // "Veintiuna"
tw.convert(200, { gender: 'feminine' }); // "Doscientas"

// Portuguese
const pt = new ToWords({ localeCode: 'pt-BR' });
pt.convert(2, { gender: 'feminine' }); // "Duas"

// Arabic
const ar = new ToWords({ localeCode: 'ar-AE' });
ar.convert(3, { gender: 'feminine' }); // "ثلاث"

Gender can also be set via constructor options and overridden per call:

const tw = new ToWords({
  localeCode: 'es-ES',
  converterOptions: { gender: 'feminine' },
});
tw.convert(1); // "Una" (constructor default)
tw.convert(1, { gender: 'masculine' }); // "Uno" (per-call override)

Supported locales: Spanish (7), Portuguese (4), Arabic (4), Hebrew (2), Russian, Ukrainian, Polish, Czech, Croatian, Slovak, Serbian, Belarusian, Bulgarian, Catalan, Romanian, Latvian, Lithuanian, and Slovenian.

UseAnd Option

Insert the locale's "And" word before the last two digits:

const tw = new ToWords({ localeCode: 'en-US' });
tw.convert(123); // "One Hundred Twenty Three"
tw.convert(123, { useAnd: true }); // "One Hundred And Twenty Three"
tw.convert(1023, { useAnd: true }); // "One Thousand And Twenty Three"

// Works with currency too
tw.convert(123, { currency: true, useAnd: true });
// "One Hundred And Twenty Three Dollars Only"

Note: useAnd is a no-op for locales that already use a split word (e.g., Portuguese uses "E" by default) and for locales where the connector token is empty (e.g., ja-JP, zh-CN, zh-TW, yue-HK).

Formal Chinese Numerals

Use formal/financial characters (大写/大寫) for Chinese locales:

// Simplified Chinese
const cn = new ToWords({ localeCode: 'zh-CN' });
cn.convert(123); // "百 二十 三"
cn.convert(123, { formal: true }); // "佰 贰拾 叁"
cn.convert(100, { currency: true, formal: true });
// "佰 圆 整"

// Traditional Chinese
const tw = new ToWords({ localeCode: 'zh-TW' });
tw.convert(123, { formal: true }); // "佰 貳拾 參"
tw.toOrdinal(5, { formal: true }); // "第伍"

Tree-Shakeable Imports

Every locale entry point (to-words/<locale>) exports four things:

| Export | Type | Description | | ------------ | -------- | --------------------------------------------- | | ToWords | class | Full class API pre-configured for this locale | | toWords | function | Convert number → words | | toOrdinal | function | Convert number → ordinal words | | toCurrency | function | Convert number → currency words |

// Class-based (locale pre-configured, no localeCode needed)
import { ToWords } from 'to-words/en-US';
const tw = new ToWords();
tw.convert(12345); // "Twelve Thousand Three Hundred Forty Five"

// Functional helpers (locale baked in — smallest possible import)
import { toWords, toOrdinal, toCurrency } from 'to-words/en-US';
toWords(12345); // "Twelve Thousand Three Hundred Forty Five"
toOrdinal(3); // "Third"
toCurrency(100); // "One Hundred Dollars Only"

Individual imports are substantially smaller than the full bundle. See the measured bundle sizes.

Locale Capability Manifest

Feature discovery is available through an opt-in entry point:

import { getLocaleCapabilities, getLocaleMetadata, isSupportedLocale, SUPPORTED_LOCALES } from 'to-words/manifest';

isSupportedLocale('en-US'); // true
getLocaleCapabilities('zh-CN')?.formal; // true
getLocaleMetadata('hi-IN')?.numbering.grouping; // [3, 2]
getLocaleMetadata('en-US')?.range.maximumSupported.cardinal; // exact inclusive ceiling
SUPPORTED_LOCALES.length; // 136

The manifest contains compact generated capability, numbering-system, and range metadata without loading locale conversion tables. Custom locale classes passed to the full ToWords class or ToWordsCore are validated automatically on first use; authors can also call assertLocaleConfig() from to-words/locale-contract in CI. Per-locale entry points use smaller, prevalidated built-in tables. See the generated capability matrix and locale quality gates.

Browser Usage (UMD)

<!-- Single locale (recommended for smaller bundles) -->
<script src="https://cdn.jsdelivr.net/npm/to-words/dist/umd/en-US.min.js"></script>
<script>
  // ToWords is pre-configured for en-US
  const toWords = new ToWords();
  console.log(toWords.convert(12345));
  // "Twelve Thousand Three Hundred Forty Five"
</script>

<!-- Full bundle with all locales -->
<script src="https://cdn.jsdelivr.net/npm/to-words/dist/umd/to-words.min.js"></script>
<script>
  // Specify locale when using full bundle
  const toWords = new ToWords({ localeCode: 'fr-FR' });
  console.log(toWords.convert(12345));
  // "Douze Mille Trois Cent Quarante-Cinq"
</script>

Functional API

Two flavours depending on whether you need tree-shaking:

Full bundle — localeCode is optional; omit it to use the auto-detected runtime locale:

import { toWords, toOrdinal, toCurrency } from 'to-words';

// Explicit locale
toWords(12345, { localeCode: 'en-US' });
// "Twelve Thousand Three Hundred Forty Five"

toOrdinal(21, { localeCode: 'en-US' });
// "Twenty First"

toCurrency(1234.56, { localeCode: 'en-IN' });
// "One Thousand Two Hundred Thirty Four Rupees And Fifty Six Paise Only"

// No localeCode — uses detectLocale() automatically
toWords(12345);
// result depends on the runtime locale (e.g. 'en-US' → "Twelve Thousand Three Hundred Forty Five")

toCurrency(1234.56, { doNotAddOnly: true });
// currency in the runtime locale, without "Only" suffix

Per-locale import — locale baked in, no localeCode argument at all, fully tree-shakeable:

import { toWords, toOrdinal, toCurrency } from 'to-words/en-US';

toWords(12345); // "Twelve Thousand Three Hundred Forty Five"
toOrdinal(21); // "Twenty First"
toCurrency(1234.56); // "One Thousand Two Hundred Thirty Four Dollars And Fifty Six Cents Only"

Performance note: The functional API caches one ToWords instance per locale. Repeated calls for the same locale reuse the cached instance.

Auto-Detect Locale

detectLocale() is automatically used by new ToWords(), toWords(), toOrdinal(), and toCurrency() when no localeCode is provided — so in most cases you don't need to call it directly. resolveLocale() applies the same matching rules to a dynamic string without reading the environment.

import { detectLocale, resolveLocale, toWords, ToWords } from 'to-words';

// Used implicitly — no localeCode needed
toWords(1000);
// On a browser with navigator.language = 'fr-FR': "Mille"
// In a Node.js process with fr-FR locale:         "Mille"
// Fallback when nothing can be detected:           "One Thousand" (en-IN)

// Used explicitly — read once, reuse across many calls
const locale = detectLocale('en-US'); // custom fallback if detection misses
const tw = new ToWords({ localeCode: locale });
tw.convert(1000);

const requestLocale = resolveLocale('EN_us'); // 'en-US'

Locale matching canonicalises BCP 47 casing and aliases, ignores script subtags when matching a supported language-region pair, and uses deterministic defaults for language-only values (en → en-US, es → es-ES, pt → pt-BR). In SSR and APIs, pass the request locale explicitly; setLocaleDetector() changes process-wide state and is intended for tests or application-wide configuration.

Reads navigator.language in browsers, Intl.DateTimeFormat().resolvedOptions().locale in Node.js (and compatible runtimes). Falls back to 'en-IN' (or your custom fallback) if the detected value cannot be matched to a supported locale.

🔄 Migration Guide

Migrating from number-to-words, written-number, num-words, or n2words? Here's how to-words compares:

| Capability | to-words | number-to-words | written-number | num-words | n2words | | -------------------------- | --------------- | --------------- | -------------- | -------------- | ------------- | | Locale / language coverage | 136 locales | English-focused | Multi-language | Indian English | 70+ languages | | TypeScript declarations | ✅ | ❌ | ❌ | ✅ | ✅ | | ESM-ready package | ✅ | ❌ | ❌ | ❌ | ✅ | | Package exports map | ✅ | ❌ | ❌ | ❌ | ✅ | | BigInt support | ✅ | ❌ | ❌ | ❌ | ✅ | | Currency conversion mode | ✅ | ❌ | ❌ | ❌ | ✅ | | Ordinal conversion | ✅ | ✅ | ❌ | ❌ | ✅ | | Subpath locale imports | ✅ | ❌ | ❌ | ❌ | ✅ |

• See MIGRATION.md for side-by-side API mapping and migration recipes.
• Includes package comparison, behavior notes, and a regression checklist.
• Deeper breakdown: docs comparison page.

🖥️ CLI

Run one-off conversions from the command line without installing:

npx to-words 12345
# Twelve Thousand Three Hundred Forty Five

npx to-words 12345 --locale en-US
# Twelve Thousand Three Hundred Forty Five

npx to-words 1234.56 --locale en-US --currency
# One Thousand Two Hundred Thirty Four Dollars And Fifty Six Cents Only

npx to-words 3 --locale en-US --ordinal
# Third

npx to-words --locale en-US -- -5
# Minus Five

npx to-words --detect-locale
# en-US  (or whatever your system locale is)

Once installed globally (npm i -g to-words), the to-words command is available directly.

⚛️ Framework Integration

React

// Change the locale import to match your users' region (e.g. 'to-words/en-GB' for UK)
import { ToWords } from 'to-words/en-US';

const toWords = new ToWords();

function PriceInWords({ amount }: { amount: number }) {
  const words = toWords.convert(amount, { currency: true });
  return <span className="price-words">{words}</span>;
}

// Usage: <PriceInWords amount={1234.56} />
// Renders: "One Thousand Two Hundred Thirty Four Dollars And Fifty Six Cents Only"

Vue 3

<script setup lang="ts">
import { computed } from 'vue';
import { ToWords } from 'to-words/en-US';

const props = defineProps<{ amount: number }>();
const toWords = new ToWords();

const words = computed(() => toWords.convert(props.amount, { currency: true }));
</script>

<template>
  <span class="price-words">{{ words }}</span>
</template>

Angular

import { Pipe, PipeTransform } from '@angular/core';
import { ToWords } from 'to-words/en-US';

@Pipe({ name: 'toWords', standalone: true })
export class ToWordsPipe implements PipeTransform {
  private toWords = new ToWords();

  transform(value: number, currency = false): string {
    return this.toWords.convert(value, { currency });
  }
}

// Usage: {{ 1234.56 | toWords:true }}

Svelte

<script lang="ts">
  import { ToWords } from 'to-words/en-US';

  export let amount: number;

  const toWords = new ToWords();
  $: words = toWords.convert(amount, { currency: true });
</script>

<span class="price-words">{words}</span>

Next.js

// Server Component (App Router) — locale from request headers or user profile
import { toWords } from 'to-words';

type Props = { amount: number; locale: string };

export default function AmountInWords({ amount, locale }: Props) {
  return <p>{toWords(amount, { localeCode: locale, currency: true })}</p>;
}

// Client Component — dynamic locale switching
'use client';

import { useState } from 'react';
import { toCurrency, detectLocale } from 'to-words';

export function CurrencyDisplay({ amount }: { amount: number }) {
  const [locale, setLocale] = useState(detectLocale('en-US'));
  return (
    <div>
      <select value={locale} onChange={(e) => setLocale(e.target.value)}>
        <option value="en-US">English (US)</option>
        <option value="fr-FR">French</option>
        <option value="hi-IN">Hindi</option>
        <option value="ar-AE">Arabic</option>
      </select>
      <p>{toCurrency(amount, { localeCode: locale })}</p>
    </div>
  );
}

Node.js / Express

import express from 'express';
import { toWords, toCurrency } from 'to-words';

const app = express();

app.get('/convert', (req, res) => {
  const number = String(req.query.number ?? '');
  const locale = String(req.query.locale ?? req.headers['accept-language']?.split(',')[0] ?? 'en-US');
  const currency = req.query.currency === 'true';

  try {
    const result = currency ? toCurrency(number, { localeCode: locale }) : toWords(number, { localeCode: locale });
    res.json({ result, locale });
  } catch (e) {
    res.status(400).json({ error: (e as Error).message });
  }
});

🌍 Numbering Systems

Different regions use different numbering systems. This library supports all major systems:

Short Scale (Western)

Used in: USA, UK, Canada, Australia, and most English-speaking countries.

| Number | Name | | ------ | ------------ | | 10^6 | Million | | 10^9 | Billion | | 10^12 | Trillion | | 10^15 | Quadrillion | | ... | ... | | 10^63 | Vigintillion |

const toWords = new ToWords({ localeCode: 'en-US' });
toWords.convert(1000000000000000000n);
// "One Quintillion"

Long Scale (European)

Used in: Germany, France, and many European countries.

| Number | German | French | | ------ | --------- | -------- | | 10^6 | Million | Million | | 10^9 | Milliarde | Milliard | | 10^12 | Billion | Billion | | 10^15 | Billiarde | Billiard |

const toWords = new ToWords({ localeCode: 'de-DE' });
toWords.convert(1000000000);
// "Eins Milliarde"

Indian System

Used in: India, Bangladesh, Nepal, Pakistan.

| Number | Name | | ------ | ------ | | 10^5 | Lakh | | 10^7 | Crore | | 10^9 | Arab | | 10^11 | Kharab | | 10^13 | Neel | | 10^15 | Padma | | 10^17 | Shankh |

const toWords = new ToWords({ localeCode: 'en-IN' });
toWords.convert(100000000000000000n);
// "One Shankh"

const toWordsHindi = new ToWords({ localeCode: 'hi-IN' });
toWordsHindi.convert(100000000000000000n);
// "एक शंख"

East Asian System

Used in: Japan, China, Korea.

| Number | Character | | ------ | ------------- | | 10^4 | 万 (Man/Wan) | | 10^8 | 億 (Oku/Yi) | | 10^12 | 兆 (Chō/Zhao) | | 10^16 | 京 (Kei/Jing) | | 10^20 | 垓 (Gai) |

const toWords = new ToWords({ localeCode: 'ja-JP' });
toWords.convert(100000000);
// "一 億"

⚙️ API Reference

Constructor Options

interface BundledToWordsOptions {
  localeCode?: LocaleCode; // Default: auto-detected, then falls back to 'en-IN'
  converterOptions?: {
    currency?: boolean; // Default: false
    ignoreDecimal?: boolean; // Default: false
    ignoreZeroCurrency?: boolean; // Default: false
    doNotAddOnly?: boolean; // Default: false
    includeZeroFractional?: boolean; // Default: false
    rangeMode?: 'strict' | 'compose'; // Default: 'strict'
    currencyOptions?: {
      name: string;
      plural: string;
      symbol: string;
      precision?: number; // decimal places for fractional unit; defaults to 2
      fractionalUnit: {
        name: string;
        plural: string;
        symbol: string;
      };
    };
  };
}

Class Methods

convert(number, options?)

Converts a number to words.

• number: number | bigint | string — The number to convert
• options: ConverterOptions — Override instance options
• returns: string — The number in words

toOrdinal(number, options?)

Converts a number to ordinal words.

• number: number | bigint | string — The number to convert (must be a non-negative integer value)
• options: OrdinalOptions — Optional settings ({ formal?: boolean; gender?: 'masculine' | 'feminine' })
• returns: string — The ordinal in words (e.g., "First", "Twenty Third")

Functional Exports

The three conversion helpers (toWords, toOrdinal, toCurrency) are available from the full bundle (to-words) and from every per-locale entry point (to-words/<locale>). detectLocale is only available from the full bundle. When importing from to-words/<locale>, the locale is already baked in and localeCode is not accepted.

toWords(number, options?)

Converts a number to words.

• number: number | bigint | string — The number to convert
• options (full bundle): ConverterOptions & { localeCode?: LocaleCode } — When localeCode is omitted, detectLocale() is called automatically
• options (per-locale): ConverterOptions
• returns: string

import { toWords } from 'to-words';
toWords(12345, { localeCode: 'en-US' }); // explicit locale
toWords(12345); // auto-detects runtime locale

import { toWords } from 'to-words/en-US';
toWords(12345); // locale baked in, no detection needed

toOrdinal(number, options?)

Converts a number to ordinal words.

• number: number | bigint | string — Must represent a non-negative integer
• options (full bundle): OrdinalOptions & { localeCode?: LocaleCode } — When localeCode is omitted, detectLocale() is called automatically
• options (per-locale): OrdinalOptions
• returns: string

import { toOrdinal } from 'to-words';
toOrdinal(21, { localeCode: 'en-US' }); // explicit locale
toOrdinal(21); // auto-detects runtime locale

import { toOrdinal } from 'to-words/en-US';
toOrdinal(21); // locale baked in

toCurrency(number, options?)

Shorthand for converting a number to currency words. Equivalent to toWords(number, { currency: true, ...options }).

• number: number | bigint | string
• options (full bundle): ConverterOptions & { localeCode?: LocaleCode } — When localeCode is omitted, detectLocale() is called automatically
• options (per-locale): ConverterOptions
• returns: string

import { toCurrency } from 'to-words';
toCurrency(1234.56, { localeCode: 'en-US' }); // explicit locale
toCurrency(1234.56); // auto-detects runtime locale

import { toCurrency } from 'to-words/en-US';
toCurrency(1234.56); // locale baked in

detectLocale(fallback?)

Reads the current runtime locale.

• In browsers: reads navigator.language

• In Node.js (and compatible runtimes): reads Intl.DateTimeFormat().resolvedOptions().locale

• Normalises BCP 47 tags (e.g. zh-Hant-TW → zh-TW) and falls back to a language-prefix match

• fallback (optional): LocaleCode — Returned when no supported locale can be matched. Default: 'en-IN'

• returns: LocaleCode — A supported locale code

Matching canonicalises BCP 47 casing and aliases. Language-only or unknown-region inputs use explicit defaults rather than registry order, including en → en-US, es → es-ES, pt → pt-BR, and sw → sw-KE.

import { detectLocale } from 'to-words';

detectLocale(); // e.g. 'en-US', 'fr-FR', 'ja-JP'
detectLocale('en-GB'); // custom fallback if detection fails

detectLocale is only available from the full bundle (to-words), not from per-locale entry points.

resolveLocale(input)

Canonicalises and matches a dynamic BCP 47 string without reading the environment. It returns LocaleCode | undefined, making it the safe bridge between user/request data and the typed constructor/helpers.

import { resolveLocale, ToWords } from 'to-words';

const localeCode = resolveLocale('zh-Hant-TW'); // 'zh-TW'
if (localeCode) new ToWords({ localeCode });

setLocaleDetector() changes a process-wide detector and is intended for tests or application-wide configuration. Do not change it per SSR/API request; pass { localeCode } explicitly instead.

Utility Methods

• toFixed(number, precision?) returns a number rounded with decimal arithmetic (toFixed(1.005, 2) === 1.01).
• isFloat(number) returns whether a valid number | bigint | string has a non-zero fractional component.
• isNumberZero(number) returns true only for exact numeric zero.
• getLocale().config is available for inspection and is recursively frozen after initialization. Define custom locale data before passing its class to setLocale().
• resolveLocale(input) returns a supported canonical LocaleCode or undefined without reading runtime globals.

LOCALES, DefaultToWordsOptions, and DefaultConverterOptions are frozen. Constructor options, including nested currency data, are snapshotted when an instance is created.

Converter Options

| Option | Type | Default | Description | | ----------------------- | ------- | ---------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | currency | boolean | false | Convert as currency with locale-specific formatting | | ignoreDecimal | boolean | false | Ignore fractional part when converting | | ignoreZeroCurrency | boolean | false | Skip zero main currency (e.g., show only "Thirty Six Paise") | | doNotAddOnly | boolean | false | Omit "Only" suffix in currency mode | | includeZeroFractional | boolean | false | When input is a string like "123.00", include "And Zero Paise" even though the decimal is zero | | currencyOptions | object | undefined | Override locale's default currency settings | | gender | string | undefined | Grammatical gender: 'masculine' or 'feminine'. Applies to locales with gendered number words | | useAnd | boolean | undefined | Insert the locale connector before the last two digits (e.g., "One Hundred And Twenty Three"). No-op when locale already defines a split word or has an empty connector token | | formal | boolean | undefined | Use formal/financial characters (currently supported for zh-CN and zh-TW) | | decimalStyle | string | 'digit' | Decimal rendering style: 'digit' (default — digit-by-digit after the point) or 'fraction' (positional/legal style — "Forty-Five Hundredths"). See Fraction Style for locale support. | | rangeMode | string | 'strict' | 'strict' enforces the locale's form-specific ceiling; 'compose' opts into legacy recursive scale composition. |

Common Options Example

const toWords = new ToWords({ localeCode: 'en-US' });

toWords.convert(1234.56, {
  currency: true,
  ignoreDecimal: false,
  doNotAddOnly: true,
});
// "One Thousand Two Hundred Thirty Four Dollars And Fifty Six Cents"

🔢 Spelled-Out Decimal (Fraction Style)

By default, decimals are rendered digit-by-digit after the point word:

const tw = new ToWords({ localeCode: 'en-US' });
tw.convert(123.45); // "One Hundred Twenty Three Point Four Five"

Pass decimalStyle: 'fraction' to use the positional/legal style used in financial and legal writing — the fractional part is converted as a whole number followed by its place-value denominator:

tw.convert(123.45, { decimalStyle: 'fraction' });
// "One Hundred Twenty Three And Forty Five Hundredths"

tw.convert(1.1, { decimalStyle: 'fraction' }); // "One And One Tenth"
tw.convert(0.05, { decimalStyle: 'fraction' }); // "Zero And Five Hundredths"
tw.convert(0.001, { decimalStyle: 'fraction' }); // "Zero And One Thousandth"

The denominator is singular when the fractional value equals 1 and plural otherwise. Russian, Ukrainian, and Belarusian follow the Slavic rule (n % 10 === 1 && n % 100 !== 11):

const ru = new ToWords({ localeCode: 'ru-RU' });
ru.convert(1.21, { decimalStyle: 'fraction' }); // "...Двадцать Один Сотая"   (singular)
ru.convert(1.11, { decimalStyle: 'fraction' }); // "...Одиннадцать Сотых"     (plural)

Fallback: if the locale has no denominator word for the given decimal length (e.g., 7+ digits), it automatically falls back to the default digit-by-digit style — no error thrown.

Supported denominator lengths

| Decimal places | English denominator | French denominator | German denominator | | -------------- | ---------------------------------------- | ------------------------------ | ------------------ | | 1 | Tenth / Tenths | Dixième / Dixièmes | Zehntel | | 2 | Hundredth / Hundredths | Centième / Centièmes | Hundertstel | | 3 | Thousandth / Thousandths | Millième / Millièmes | Tausendstel | | 4 | Ten-Thousandth / Ten-Thousandths | Dix-Millième / Dix-Millièmes | Zehntausendstel | | 5 | Hundred-Thousandth / Hundred-Thousandths | Cent-Millième / Cent-Millièmes | Hunderttausendstel | | 6 | Millionth / Millionths | Millionième / Millionièmes | Millionstel |

Locale support (100 locales)

| Language group | Locales | | -------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | English | en-AE, en-AU, en-BD, en-CA, en-GB, en-GH, en-HK, en-IE, en-IN, en-IQ, en-JM, en-KE, en-LK, en-MA, en-MM, en-MU, en-MY, en-NG, en-NP, en-NZ, en-OM, en-PH, en-PK, en-SA, en-SG, en-TT, en-TZ, en-UG, en-US, en-ZA, en-ZW | | German | de-AT, de-CH, de-DE | | French | fr-BE, fr-CA, fr-CH, fr-CI, fr-CM, fr-DZ, fr-FR, fr-MA, fr-MG, fr-SA | | Spanish | es-AR, es-CL, es-CO, es-ES, es-MX, es-PE, es-US, es-VE | | Portuguese | pt-AO, pt-BR, pt-MZ, pt-PT | | Italian | it-IT | | Dutch | nl-NL, nl-SR | | Scandinavian | da-DK, nb-NO, sv-SE | | Other European | bg-BG, ca-ES, cs-CZ, el-GR, hr-HR, hu-HU, lv-LV, pl-PL, ro-RO, sk-SK, sl-SI, sq-AL, sr-RS | | Slavic (with Slavic singular rule) | be-BY, ru-RU, uk-UA | | Indic | as-IN, bn-BD, bn-IN, gu-IN, hi-IN, kn-IN, ml-IN, mr-IN, ne-NP, or-IN, pa-IN, ta-IN, te-IN | | Others | af-ZA, fa-IR, he-IL, id-ID, ka-GE, ms-MY, ms-SG, ur-PK, vi-VN |

Locales not listed above (Arabic, East Asian, Turkic, etc.) do not yet support decimalStyle: 'fraction' — passing the option silently falls back to digit-by-digit.

📏 Bundle Sizes

| Import Method | Raw | Gzip | | ------------------------- | -------- | -------- | | Full bundle (all locales) | 703 KiB | 70.4 KiB | | Single locale (en-US) | 19.5 KiB | 5.5 KiB | | Single locale (en-IN) | 17.2 KiB | 5.3 KiB |

Tip: Use tree-shakeable imports or single-locale UMD bundles for the smallest bundle size.

The build enforces gzip budgets for the full bundle, average locale, and largest locale. Run npm run size:check to inspect the current measurements locally.

⚡ Performance

Benchmarked on Apple M2 (Node.js 23):

| Operation | Throughput | | -------------------------- | ------------- | | Small integers (42) | ~4.7M ops/sec | | Medium integers (12,345) | ~2.2M ops/sec | | Large integers (15 digits) | ~700K ops/sec | | Currency conversion | ~1M ops/sec | | BigInt (30+ digits) | ~225K ops/sec |

Run benchmarks locally:

npm run bench

🌐 Browser Compatibility

| Browser | Version | | ------- | ------- | | Chrome | 67+ | | Firefox | 68+ | | Safari | 14+ | | Edge | 79+ | | Opera | 54+ |

BigInt Support: BigInt is required for full functionality. Internet Explorer is not supported.

Runtime Compatibility

| Runtime | Support | | ------------------ | ----------------------------- | | Node.js | 20+ (CI-verified) | | Deno | ✅ compatible by architecture | | Bun | ✅ compatible by architecture | | Cloudflare Workers | ✅ compatible by architecture |

Deno, Bun, and Cloudflare Workers are compatible by architecture: the library uses only standard ECMAScript features (BigInt, Intl, Map, globalThis) with zero Node.js-specific APIs. Only Node.js is covered by CI.

🗺️ Supported Locales

All 136 locales with their core setup are listed below. Numbering-system, grouping, and named-range metadata is maintained in the generated capability matrix rather than duplicated here.

| Locale | Language | Country | Currency | Ordinal | | ------ | --------------- | ------------------- | ------------- | ------- | | af-ZA | Afrikaans | South Africa | Rand | ✓ | | am-ET | Amharic | Ethiopia | ብር | ✓ | | ar-AE | Arabic | UAE | درهم | ✓ | | ar-DZ | Arabic | Algeria | دينار | ✓ | | ar-EG | Arabic | Egypt | جنيه | ✓ | | ar-IQ | Arabic | Iraq | دينار | ✓ | | ar-LB | Arabic | Lebanon | ليرة | ✓ | | ar-MA | Arabic | Morocco | درهم | ✓ | | ar-SA | Arabic | Saudi Arabia | ريال | ✓ | | ar-SD | Arabic | Sudan | جنيه | ✓ | | ar-YE | Arabic | Yemen | ريال | ✓ | | as-IN | Assamese | India | টকা | ✓ | | az-AZ | Azerbaijani | Azerbaijan | Manat | ✓ | | be-BY | Belarusian | Belarus | Рубель | ✓ | | bg-BG | Bulgarian | Bulgaria | Лев | ✓ | | bn-BD | Bengali | Bangladesh | টাকা | ✓ | | bn-IN | Bengali | India | টাকা | ✓ | | ca-ES | Catalan | Spain | Euro | ✓ | | cs-CZ | Czech | Czech Republic | Koruna | ✓ | | da-DK | Danish | Denmark | Krone | ✓ | | de-AT | German | Austria | Euro | ✓ | | de-CH | German | Switzerland | Franken | ✓ | | de-DE | German | Germany | Euro | ✓ | | el-GR | Greek | Greece | Ευρώ | ✓ | | en-AE | English | UAE | Dirham | ✓ | | en-AU | English | Australia | Dollar | ✓ | | en-BD | English | Bangladesh | Taka | ✓ | | en-CA | English | Canada | Dollar | ✓ | | en-GB | English | United Kingdom | Pound | ✓ | | en-GH | English | Ghana | Cedi | ✓ | | en-HK | English | Hong Kong | Dollar | ✓ | | en-IE | English | Ireland | Euro | ✓ | | en-IN | English | India | Rupee | ✓ | | en-IQ | English | Iraq | Dinar | ✓ | | en-JM | English | Jamaica | Dollar | ✓ | | en-KE | English | Kenya | Shilling | ✓ | | en-LK | English | Sri Lanka | Rupee | ✓ | | en-MA | English | Morocco | Dirham | ✓ | | en-MM | English | Myanmar | Kyat | ✓ | | en-MU | English | Mauritius | Rupee | ✓ | | en-MY | English | Malaysia | Ringgit | ✓ | | en-NG | English | Nigeria | Naira | ✓ | | en-NP | English | Nepal | Rupee | ✓ | | en-NZ | English | New Zealand | Dollar | ✓ | | en-OM | English | Oman | Rial | ✓ | | en-PH | English | Philippines | Peso | ✓ | | en-PK | English | Pakistan | Rupee | ✓ | | en-SA | English | Saudi Arabia | Riyal | ✓ | | en-SG | English | Singapore | Dollar | ✓ | | en-TT | English | Trinidad and Tobago | Dollar | ✓ | | en-TZ | English | Tanzania | Shilling | ✓ | | en-UG | English | Uganda | Shilling | ✓ | | en-US | English | USA | Dollar | ✓ | | en-ZA | English | South Africa | Rand | ✓ | | en-ZW | English | Zimbabwe | Zimbabwe Gold | ✓ | | es-AR | Spanish | Argentina | Peso | ✓ | | es-CL | Spanish | Chile | Peso | ✓ | | es-CO | Spanish | Colombia | Peso | ✓ | | es-ES | Spanish | Spain | Euro | ✓ | | es-MX | Spanish | Mexico | Peso | ✓ | | es-PE | Spanish | Peru | Sol | ✓ | | es-US | Spanish | USA | Dólar | ✓ | | es-VE | Spanish | Venezuela | Bolívar | ✓ | | et-EE | Estonian | Estonia | Euro | ✓ | | fa-IR | Persian | Iran | تومان | ✓ | | fi-FI | Finnish | Finland | Euro | ✓ | | fil-PH | Filipino | Philippines | Piso | ✓ | | fr-BE | French | Belgium | Euro | ✓ | | fr-CA | French | Canada | Dollar | ✓ | | fr-CH | French | Switzerland | Franc | ✓ | | fr-CI | French | Côte d'Ivoire | Franc CFA | ✓ | | fr-CM | French | Cameroon | Franc CFA | ✓ | | fr-DZ | French | Algeria | Dinar | ✓ | | fr-FR | French | France | Euro | ✓ | | fr-MA | French | Morocco | Dirham | ✓ | | fr-MG | French | Madagascar | Ariary | ✓ | | fr-SA | French | Saudi Arabia | Riyal | ✓ | | gu-IN | Gujarati | India | રૂપિયો | ✓ | | ha-NG | Hausa | Nigeria | Naira | ✓ | | hbo-IL | Biblical Hebrew | Israel | שקל | ✓ | | he-IL | Hebrew | Israel | שקל | ✓ | | hi-IN | Hindi | India | रुपया | ✓ | | hr-HR | Croatian | Croatia | Euro | ✓ | | hu-HU | Hungarian | Hungary | Forint | ✓ | | id-ID | Indonesian | Indonesia | Rupiah | ✓ | | ig-NG | Igbo | Nigeria | Naira | ✓ | | is-IS | Icelandic | Iceland | Króna | ✓ | | it-IT | Italian | Italy | Euro | ✓ | | ja-JP | Japanese | Japan | 円 | ✓ | | jv-ID | Javanese | Indonesia | Rupiah | ✓ | | ka-GE | Georgian | Georgia | ლარი | ✓ | | km-KH | Khmer | Cambodia | រៀល | ✓ | | kn-IN | Kannada | India | ರೂಪಾಯಿ | ✓ | | ko-KR | Korean | South Korea | 원 | ✓ | | lo-LA | Lao | Laos | ກີບ | ✓ | | lt-LT | Lithuanian | Lithuania | Euras | ✓ | | lv-LV | Latvian | Latvia | Eiro | ✓ | | ml-IN | Malayalam | India | രൂപ | ✓ | | mr-IN | Marathi | India | रुपया | ✓ | | ms-MY | Malay | Malaysia | Ringgit | ✓ | | ms-SG | Malay | Singapore | Dolar | ✓ | | my-MM | Burmese | Myanmar | ကျပ် | ✓ | | nb-NO | Norwegian | Norway | Krone | ✓ | | nl-NL | Dutch | Netherlands | Euro | ✓ | | nl-SR | Dutch | Suriname | Dollar | ✓ | | ne-NP | Nepali | Nepal | रुपैयाँ | ✓ | | or-IN | Odia | India | ଟଙ୍କା | ✓ | | pa-IN | Punjabi | India | ਰੁਪਇਆ | ✓ | | pl-PL | Polish | Poland | Złoty | ✓ | | pt-AO | Portuguese | Angola | Kwanza | ✓ | | pt-BR | Portuguese | Brazil | Real | ✓ | | pt-MZ | Portuguese | Mozambique | Metical | ✓ | | pt-PT | Portuguese | Portugal | Euro | ✓ | | ro-RO | Romanian | Romania | Leu | ✓ | | ru-RU | Russian | Russia | Рубль | ✓ | | si-LK | Sinhala | Sri Lanka | රුපියල | ✓ | | sk-SK | Slovak | Slovakia | Euro | ✓ | | sl-SI | Slovenian | Slovenia | Euro | ✓ | | sq-AL | Albanian | Albania | Lek | ✓ | | sr-RS | Serbian | Serbia | Dinar | ✓ | | sv-SE | Swedish | Sweden | Krona | ✓ | | sw-KE | Swahili | Kenya | Shilingi | ✓ | | sw-TZ | Swahili | Tanzania | Shilingi | ✓ | | ta-IN | Tamil | India | ரூபாய் | ✓ | | te-IN | Telugu | India | రూపాయి | ✓ | | th-TH | Thai | Thailand | บาท | ✓ | | tr-TR | Turkish | Turkey | Lira | ✓ | | uk-UA | Ukrainian | Ukraine | Гривня | ✓ | | ur-PK | Urdu | Pakistan | روپیہ | ✓ | | uz-UZ | Uzbek | Uzbekistan | So'm | ✓ | | vi-VN | Vietnamese | Vietnam | Đồng | ✓ | | yo-NG | Yoruba | Nigeria | Naira | ✓ | | yue-HK | Cantonese | Hong Kong | 元 | ✓ | | zh-CN | Chinese | China | 元 | ✓ | | zh-TW | Chinese | Taiwan | 元 | ✓ | | zu-ZA | Zulu | South Africa | Rand | ✓ |

Gender Support:

The following locales support grammatical gender via { gender: 'feminine' } or { gender: 'masculine' }:

• Spanish: es-ES, es-MX, es-CO, es-CL, es-AR, es-VE, es-US
• Portuguese: pt-BR, pt-PT, pt-AO, pt-MZ
• Arabic: ar-AE, ar-DZ, ar-EG, ar-IQ, ar-LB, ar-MA, ar-SA, ar-SD, ar-YE
• Hebrew: he-IL, hbo-IL
• Slavic: ru-RU, uk-UA, pl-PL, cs-CZ, hr-HR, sk-SK, sr-RS, be-BY, bg-BG
• Other: ca-ES, ro-RO, lv-LV, lt-LT, sl-SI

Formal Numerals: zh-CN and zh-TW support formal/financial Chinese characters (大写/大寫) via { formal: true }.

Scale-First Ordering: ig-NG uses scale-first word ordering (e.g., "Puku Abụọ" = "Thousand Two" for 2000).

⚠️ Error Handling

The library throws descriptive errors for invalid inputs:

Invalid Number

toWords.convert('abc');
// Error: Invalid Number "abc"

toWords.convert(NaN);
// Error: Invalid Number "NaN"

toWords.convert(Infinity);
// Error: Invalid Number "Infinity"

Unknown Locale

const toWords = new ToWords({ localeCode: 'xx-XX' });
toWords.convert(123);
// Error: Unknown Locale "xx-XX"

Invalid Ordinal Input

toWords.toOrdinal(-5);
// Error: Ordinal numbers must be non-negative integers, got "-5"

toWords.toOrdinal(3.14);
// Error: Ordinal numbers must be non-negative integers, got "3.14"

Handling Errors

try {
  const words = toWords.convert(userInput);
  console.log(words);
} catch (error) {
  console.error('Conversion failed:', error.message);
}

💖 Support

If to-words is useful in your work, consider supporting ongoing maintenance through GitHub Sponsors.

After installation, npm fund to-words surfaces the same funding link from npm metadata.

🤝 Contributing

Contributions are welcome! Please read CONTRIBUTING.md for the full guide covering development setup, coding guidelines, how to add a new locale, commit message format, and the PR process.

For questions or ideas, open an issue or start a discussion.

This project follows the Contributor Covenant Code of Conduct.

❓ FAQ

Use BigInt or pass the number as a string:

// Using BigInt
toWords.convert(9007199254740993n);

// Using string
toWords.convert('9007199254740993');

JavaScript automatically converts large numbers to scientific notation. Pass them as strings or BigInt instead:

// ❌ This may give unexpected results
toWords.convert(123456789012345678901);

// ✅ Use string or BigInt
toWords.convert('123456789012345678901');
toWords.convert(123456789012345678901n);

Yes! Override the currency options:

toWords.convert(1234.56, {
  currency: true,
  currencyOptions: {
    name: 'Bitcoin',
    plural: 'Bitcoins',
    symbol: '₿',
    fractionalUnit: { name: 'Satoshi', plural: 'Satoshis', symbol: 'sat' },
  },
});
// "One Thousand Two Hundred Thirty Four Bitcoins And Fifty Six Satoshis Only"

Yes! Use the UMD bundles via CDN:

<script src="https://cdn.jsdelivr.net/npm/to-words/dist/umd/en-US.min.js"></script>
<script>
  const toWords = new ToWords();
  console.log(toWords.convert(123));
</script>

Yes. ToWordsCore exposes a setLocale() method that accepts any class implementing LocaleInterface ({ config: LocaleConfig }). No need to fork the package or submit a PR — your custom locale stays in your own codebase.

import { ToWordsCore } from 'to-words';
import type { LocaleInterface, LocaleConfig } from 'to-words';

class BitcoinLocale implements LocaleInterface {
  config: LocaleConfig = {
    currency: {
      name: 'Bitcoin',
      plural: 'Bitcoins',
      symbol: '₿',
      fractionalUnit: { name: 'Satoshi', plural: 'Satoshis', symbol: 'sat' },
    },
    texts: { and: 'And', minus: 'Minus', only: 'Only', point: 'Point' },
    numberWordsMapping: [
      { number: 1, value: 'One' },
      { number: 2, value: 'Two' },
      // ... rest of the mapping, same structure as any built-in locale
    ],
  };
}

const tw = new ToWordsCore();
tw.setLocale(BitcoinLocale);
console.log(tw.convert(2.1, { currency: true }));
// "Two Bitcoins And Ten Satoshis Only"

The easiest starting point is to copy the nearest built-in locale from src/locales/ and change only what differs. Locale configuration is recursively frozen when first initialized so cached lookup tables cannot diverge; treat it as immutable and create a new locale class when configuration changes.

See the Contributing section above. You'll need to create a locale file implementing the LocaleInterface and add tests.

📋 Changelog

See CHANGELOG.md for a detailed history of changes.

📄 License

MIT