ExactUnits

About Exact Units

A unit converter with 754 units across 61 categories, built so that the answer is right at any number of digits you care to ask for.

Who it is for

Two audiences that usually get separate tools. If you want to know how many centimeters are in six feet, the answer is on screen before you finish reading this sentence. If you are checking a tolerance stack, converting a datasheet's thermal resistance, or reconciling a US R-value against a metric U-value, the same page will give you fifty correct significant figures and tell you whether the result is exact.

How it is built

  • Astro, generating a fully static site. No server, no database.
  • Exact rational arithmetic on JavaScript BigInt, written for this project. Details here.
  • No frameworks on the client. The converter is a single custom element of a few kilobytes. There is no React, no analytics SDK, and no web font — the fastest font is the one already on your device.
  • Every answer is pre-computed. Conversion pages ship with the result already in the HTML, so they work with JavaScript disabled and there is nothing to wait for.

How it is funded

Advertising, and nothing else. The site is free, there is no account to make and nothing to buy. Ad slots reserve their space in the layout before anything loads, so ads never push content around while you are reading, and the ad script is deferred until the browser is idle so it cannot slow down the converter.

Privacy

No analytics, no cookies set by this site, no account, and nothing you type is sent anywhere — every conversion happens in your browser. The only third-party code is the ad network, which sets its own cookies subject to its own policy. Your display preferences (significant digits and notation) are kept in your browser's local storage and never leave the device.

Corrections

Conversion factors follow the SI Brochure, the 1959 international yard and pound agreement, NIST SP 811, and CODATA 2022 where a measured value is unavoidable. Each factor is stored as its definition rather than a pre-computed decimal, so it can be checked at a glance. If you find one that is wrong, it is a bug worth reporting — the whole point of the site is that the numbers are right.