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Safe Units

Build Status NPM Version MIT License

Safe Units is a type safe library for using units of measurement in TypeScript. Safe Units provides an implementation of an SI based unit system but is flexible enough to allow users to create their own unit systems which can be independent or can interoperate with the built-in units. Users can also make unit systems for any numeric type they'd like not just the JavaScript number type. This library requires TypeScript 3.2 or higher.

import { Length, Measure, meters, seconds, Time, Velocity } from "safe-units";

const length: Length = Measure.of(30, meters);
const time: Time = Measure.of(15, seconds);
const velocity: Velocity = length.over(time);

console.log(length.toString());   // 30 m
console.log(time.toString());     // 15 s
console.log(velocity.toString()); // 2 m * s^-1

const error: Velocity = length.times(time);
// ERROR: A measure of m*s isn't assignable to a measure of m/s.


⭐  Compile-time unit arithmetic for typesafe dimensional analysis (with exponents between -5 and +5)!

⭐  Large library of predefined units including metric (with prefixes), Imperial, and US customary units!

⭐  Ability to add your own unit system that can work with built-in units!

⭐  Long build times & cryptic error messages!


Safe units is written in TypeScript and should be consumed by TypeScript users to take full advantage of what it provides. In addition you will need the following:


npm install safe-units


yarn add safe-units


Unit arithmetic

import { bars, kilograms, Measure, meters, milli, seconds } from "safe-units";

const width = Measure.of(3, meters);
const height = Measure.of(4, meters);
const area = width.times(height).scale(0.5);
const hypot = Measure.sqrt(width.squared().plus(height.squared())); // 5 m

const mass = Measure.of(30, kilograms);
const mps2 = meters.per(seconds.squared());
const acceleration = Measure.of(9.8, mps2);

const force = mass.times(acceleration); // 294 N
const pressure = force.over(area); // 49 Pa
const maxPressure = Measure.of(0.5, milli(bars)); // 0.5 mbar // true

Type errors

import { Force, Length, Measure, meters, seconds, Time } from "safe-units";

const length: Length = Measure.of(10, meters);
const time: Time = Measure.of(10, seconds);;
// ERROR: Measures of different units cannot be added

// ERROR: Measures of different units cannot be subtracted

const force: Force = length.over(time);
// ERROR: Measure of m/s is not assignable to measure of kg*m/s^2

const root = Measure.sqrt(length);
// ERROR: Can't take sqrt of measure of m since it's not a perfect square

Naming units

import { days, Measure, miles, speedOfLight, yards } from "safe-units";

const furlongs = Measure.of(220, yards, "fur");

console.log(Measure.of(8, furlongs).in(miles)); // 1 mi
console.log(Measure.of(1, miles).in(furlongs)); // 8 fur

const fortnights = Measure.of(14, days, "ftn");
const megaFurlongsPerMicroFortnight = mega(furlongs)

console.log(; // 1.8026174997852542 Mfur/µftn

Deriving quantities

import { Acceleration, Measure, meters, seconds, Time } from "safe-units";

const Jerk = Acceleration.over(Time);
type Jerk = typeof Jerk;

const mps2 = meters.per(seconds.squared());
const acceleration = Measure.of(9.8, mps2);
const jerk: Jerk = acceleration.over(Measure.of(2, seconds));

console.log(jerk.toString()); // 4.9 m * s^-3

Defining dimensions

import { Area, Measure, minutes, seconds, Time } from "safe-units";

const frames = Measure.dimension("frames");

const Frames = frames;
type Frames = typeof frames;

const FrameRate = Frames.over(Time);
type FrameRate = typeof FrameRate;

const fps: FrameRate = frames.per(seconds).withSymbol("fps");

const minFrameRate = Measure.of(60, fps);

const measuredFrames = Measure.of(8000, frames);
const elapsedTime = Measure.of(2, minutes);
const measuredFps: FrameRate = measuredFrames.over(elapsedTime);

if ( {
    // Optimize

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