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The smallest & fastest library for really easy, totally type-safe unit conversions in TypeScript & JavaScript.

published npm version test coverage bundle size npm monthly downloads type definitions license CI

npm install convert
# or
yarn add convert

More installation examples below, including browser builds.

convert(5, 'miles').to('km');
convertMany('4d 16h').to('minutes');


  • Full build time and runtime validation of conversions
  • Using a web framework like Next.js or Nuxt.js? You get 0-cost build-time conversions. Convert is totally side-effect free, so conversions will be precalculated at build-time, so absolutely zero conversion code is sent to clients!
  • Works in browsers and Node.js (UMD and ESM builds will work anywhere)
  • Out of the box ES3 backwards-compatibility (CI tests on Node.js v0.9.1)
  • Absolutely tiny bundle size and 0 dependencies
  • Supports bigints without breaking on old engines


Generated API documentation for the latest version is available online.

View docs.

// ESM:
import convert from 'convert';
// CJS:
const {convert} = require('convert');

// 360 seconds into minutes
convert(360, 'seconds').to('minutes');
// -> 6

// BigInt support
convert(20n, 'hours').to('minutes');
// -> 1200n

// Format to the best unit automatically
convert(5500, 'meters').to('best');
// -> { quantity: 5.5, unit: 'km', toString: () => '5.5km' }

// We also do length, data, volume, mass, temperature, and more
convert(5, 'kilometers').to('nautical miles');
convert(12, 'pounds').to('ounces');
convert(8192, 'bytes').to('KiB');
convert(10, 'atmospheres').to('kPa');
convert(451, 'fahrenheit').to('celsius');

Converting many units

import {convertMany} from 'convert';
const {convertMany} = require('convert');

// Convert 1 day and 8 hours into ms

Converting to best unit

import convert from 'convert';
const {convert} = require('convert');

// Convert into the best unit
const duration = convert(36, 'h').to('best');
// -> { quantity: 1.5, unit: 'd', toString: () => '1.5d' }

// The toString() method means you can automatically cast the object to a string without any issues
'duration is ' + duration;
// -> duration is 1.5d

// You can also specify to use a specific kind of units (metric or imperial, metric is default)
convert(3.5, 'km').to('best'); // -> { quantity: 3.5, unit: 'km', toString: () => '3.5km' }
convert(3.5, 'km').to('best', 'metric'); // -> { quantity: 3.5, unit: 'km', toString: () => '3.5km' }
convert(3.5, 'km').to('best', 'imperial'); // -> { quantity: 2.17, unit: 'mi', toString: () => '3.5mi' }

ms shorthand

import {ms} from 'convert';
const {ms} = require('convert');

// Convert a duration into milliseconds
ms('1d 2h 30min');
// -> 95400000

// Convert milliseconds to a string
// -> '1d'


Package manager

Convert is published as convert on npm.

npm install convert
# or
yarn add convert


// This chooses which build to use depending on NODE_ENV
const {convert} = require('convert');

// You can also specify which build to use
const {convert} = require('convert/dev');
const {convert} = require('convert/prod');

ES Modules

// The production build is the default
import convert from 'convert';

// ESM does not have automatic build switching, you must explicitly import the dev build
import convert from 'convert/dev';
import convert from 'convert/prod';


Pick your favorite CDN:


<script type="module">
import convert from 'https://cdn.skypack.dev/convert@4';
import convert from 'https://esm.run/convert@4';
import convert from 'https://cdn.jsdelivr.net/npm/convert@4';
import convert from 'https://unpkg.com/convert@4';

UMD (global)

<script src="https://cdn.jsdelivr.net/npm/convert@4/dist/convert.prod.js"></script>
<script src="https://unpkg.com/convert@4/dist/convert.prod.js"></script>


Convert is better than other unit conversion libraries because it's faster and smaller than them, while having the same features. Benchmarks of popular unit conversion libraries, including Convert are available here.

Convert is the fastest, taking less than a microsecond for all functions. That's a little over 3 million convert() calls per second.

Bundle size comparison

npm bundle size of convert

npm bundle size of safe-units

npm bundle size of convert-units

npm bundle size of js-quantities

npm bundle size of uom + npm bundle size of uom-units

Generated using TypeDoc