About

What this is

This is a free library of calculators, converters and small utilities. You open a page, type your values and get the answer. There is no account to create, nothing to install and nothing to pay.

It started from a simple frustration: most online calculators either hide the formula, bury the result under advertising, or give a number with no way to tell whether it is right. Every tool here shows the formula it used, a worked example and the limits of what it can tell you.

Who it is for

Students checking homework, technicians on a shop floor, office workers converting a supplier's figures, people planning a home project, and anyone who just needs one number quickly. The engineering tools are precise enough for professional day-to-day work; the everyday tools are simple enough for anyone.

How the tools are built

All tools share one calculation engine and one unit library. That means a conversion factor exists in exactly one place on the whole site: when it is right, it is right everywhere.

Each formula is checked against published references and against worked examples with known answers before the tool is published. Automated tests run the critical tools on every build, including edge cases such as zero, negative numbers and invalid input.

Calculations run in your browser. The values you type are never sent to a server.

How it is paid for

The site is free and is funded by advertising. Ads are kept away from buttons and input fields so they cannot be clicked by accident, and they are always clearly marked as advertising.

Found a mistake?

If a result looks wrong, tell us. Include the tool, the values you entered and the answer you expected. Corrections are the fastest way to make the library better.