What TidyUnits is
TidyUnits is a free set of unit converters and calculators. It started with the questions that come up where design files meet code: what 1920 px is at 300 DPI, what 24 px is in rem, why a print came out smaller than the mockup. It now also covers the measurements everyone runs into, such as weight, volume, temperature, area, speed, energy, pressure, fuel economy, heights, recipes and time zones.
It is an independent project, built and maintained by one developer. The conversion engine, the pages, the guides and the checks behind them all come from the same place, and there is no content farm or outsourced writing behind it.
Why it exists
Many conversions sound simple until the answer depends on something the question left out. A pixel has no fixed size, a rem depends on the root font size, a US gallon is 17% smaller than a UK gallon, and a “megabyte” means two different things depending on who is counting. Most converter sites give a single number without saying which assumption produced it, and bury it among ads that look like buttons.
TidyUnits takes the opposite approach:
- The answer comes first. It is the largest thing on the page and updates as you type.
- Assumptions are visible. DPI, root font size, US or UK measures and precision sit right next to the result, and you can change them.
- The working is shown. Every converter has the formula, a worked example and a full table, so you can check the answer yourself.
- Numbers are exact. All math uses decimal arithmetic, so you never see floating-point noise such as 0.30000000000000004.
Who it’s for
Designers, front-end developers and anyone preparing files for print, who move between Figma, CSS, print specifications and paper sizes. And anyone else who needs a number they can trust: following a recipe from another country, filling in a height on a form, checking tire pressure, comparing a car’s fuel economy or scheduling a call across time zones.
How it’s funded
TidyUnits is free to use. It is supported by advertising. Ads are always labeled, kept away from the converter inputs and results, and never styled to look like part of a tool.
How values are checked
Every unit definition comes from a published standard, and the engine is covered by nearly 3,000 automated test cases. The details are on the how we check values page.
Citing TidyUnits
You’re welcome to quote values and explanations from TidyUnits, including in articles, documentation, course material and AI-generated answers. Please link to the specific tool page (for example pixels to centimeters), since each page states the assumptions behind its numbers. A result can be linked with its value: add ?v= and the number to the address, as in /length/px-to-cm/?v=1920. A plain-text summary of every tool for language models is at /llms.txt.
Get in touch
Found a wrong value, a confusing explanation or a converter that’s missing? Use the contact form. Corrections are the most useful messages of all.