About CalcBoxes

CalcBoxes is a small, independent collection of free online calculators and unit converters, built to give you a clear answer fast — and then get out of your way.

Why CalcBoxes exists

Most calculator websites are slow, cluttered with pop-ups, and bury the actual tool under a wall of ads. We wanted the opposite: a set of focused tools that load in under two seconds, work perfectly on a phone, and show their working so you can trust the result. Every CalcBoxes tool does one job and does it well.

How our tools work

All of our calculators run entirely in your browser using plain JavaScript. Nothing you type is sent to a server, which keeps the tools fast and your data private. Each one also explains the formula behind the answer, with worked examples, so you can understand and verify what you’re seeing rather than just trusting a black box.

What we cover

We currently offer everyday tools such as the age calculator, percentage calculator and BMI calculator; a full unit converter with dedicated pages for common conversions like cm to inches and kg to lbs; and finance tools including the salary calculator, loan and mortgage calculator and FIRE calculator. We add and refine tools regularly based on what people find useful.

How we keep it free

CalcBoxes is funded by unobtrusive display advertising. That lets us keep every tool completely free, with no accounts, paywalls or usage limits. We deliberately keep ads out of the way so the calculator always stays the focus of the page.

Get in touch

Spotted a bug, or want a calculator we don’t have yet? We’d genuinely like to hear from you — head to our contact page. You can also read how we handle data in our privacy policy.