Numeros
Numeros is a free online library of 400+ calculators covering finance, health, mathematics, engineering, construction, business and education.
What makes it different is transparency: every calculator displays the exact formula it uses, works through a real example step by step, and cites the published source that defined 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, and every page honestly states what the result cannot tell you and when a professional should be consulted instead.
There is no sign-up, no usage caps and no premium tier. Every calculation runs entirely in the user's browser — nothing typed is ever sent anywhere.
Built for students, engineers, builders and everyday people who want to understand their numbers, not just see them. Because a number you cannot check is a number you should not act on.
