Numeros

Numeros is a free online library of 400+ calculators covering finance, health, math, engineering, construction and education.

What makes it different: transparency. Every calculator displays the exact formula it uses, works through a real example, and cites the published source behind it — Mifflin-St Jeor for BMR, Regulation Z for APR, ACI 308R for concrete curing.

Each tool is verified against hand-computed references and tested at the boundary cases where calculators usually break. Every page honestly states what the result cannot tell you, and when a professional should be consulted instead.

No sign-up, no caps, no premium tier. 100% private — everything runs in your browser; nothing is ever sent anywhere.

For students, engineers, builders and anyone who wants to understand their numbers, not just see them. Because a number you cannot check is a number you should not act on.