bmi-logic

A tiny, dependency-free TypeScript library that computes the Body Mass Index from a weight and a height.

It exposes a single function — nothing more — so it stays small, predictable, and easy to embed in any environment (Node, browsers, edge runtimes).

Install

yarn add bmi-logic
# or
npm install bmi-logic

Usage

import { calculateBmi } from 'bmi-logic'

calculateBmi(65, 1.7)   // "22.49"
calculateBmi(75, 1.8)   // "23.15"
calculateBmi(0, 1.7)    // undefined
calculateBmi(70, -1.7)  // undefined

API

calculateBmi(weight, height)

| Parameter | Type | Description | | --------- | -------- | ------------------- | | weight | number | Weight in kilograms | | height | number | Height in meters |

Returns: string | undefined

• A two-decimal string (e.g. "22.49") when both inputs are positive numbers.
• undefined when weight or height is <= 0.

The string format is intentional: it preserves the trailing zero (e.g. "22.00") so the value can be rendered as-is in a UI. Call Number(...) if you need a numeric value.

And about the categorization?

It only produces the raw BMI value — it does not classify it.

To turn that value into a human-readable category (e.g. "Normal weight", "Overweight") or to compute an ideal weight range, pair it with bmi-utils package:

import { calculateBmi } from 'bmi-logic'
import { loadCategory, MALE } from 'bmi-utils'

const bmi = calculateBmi(75, 1.8)
const category = bmi !== undefined
  ? loadCategory(MALE, Number(bmi), 'en-US')
  : ''

console.log({ bmi, category })
// { bmi: '23.15', category: 'Normal weight' }

Author

Emanuel Gonçalves

• GitHub @emanuelgsouza
• LinkedIn @emanuelgsouza