About

wati.dev is a collection of free calculators for the questions that come up in ordinary life: what a loan really costs, how much to tip, whether 180 grams of flour is one cup or two, how many days until a deadline. Each calculator lives on its own page, loads in a fraction of a second, and shows its result the moment you finish typing.

How the calculators work

Every tool on this site runs entirely in your browser. When you type a number, nothing is sent to a server — the arithmetic happens on your device, which is why the results are instant and why the site works the same on a phone in a basement as it does on fiber.

Each page explains the formula it uses, in plain terms, right under the calculator. Where a calculation has an established or official definition — amortized loan payments, BMI, the international inch — that definition is the one implemented, and the page says where it comes from. If a result would depend on assumptions, the page states the assumptions instead of hiding them.

Principles

• The answer first. No sign-ups, no "unlock full results", no PDF exports as bait. The number you came for is the first thing on the page.
• Show the working. A calculator you cannot check is a rumor with a text box. Every page documents its formula and includes a worked example you can verify by hand.
• Respect the visitor. The numbers you type stay on your device. Preferences like dark mode and your currency are stored in your own browser and nowhere else.

Corrections

If a result looks wrong, it might be. Formulas get updated, conventions differ between countries, and bugs exist. Send a note with the calculator name and the inputs you used. Reports get read, and a correction that checks out gets made.