About Keep Calculator

Keep Calculator is a cabinet of free calculators. Each calculator is kept like a library index card: one card, one job. It takes the numbers you type, applies one standard formula and shows the answer together with the formula, what every variable means and a worked example you can repeat by hand.

The ten drawers

The cards are filed in ten drawers: unit conversions, days and time, engines and motion, electricity and signals, water, air and heat, numbers and powers, lab science, work and ops metrics, cycling and outdoors, and kitchen and party. Every card is also listed in the A to Z index, and the unit converter handles ten kinds of quantity when an input is in the wrong unit.

What a card holds

• The calculator itself, opened on a realistic worked case.
• The formula in words and symbols, with units and constants.
• A worked example that uses the default numbers step by step.
• The limits of the formula and the mistakes people make with it.
• The exact lines the calculator runs, in a “Formula used” box.

What is not kept here

The site keeps to general, checkable arithmetic. It does not publish calculators for loans, credit, tax, investments or crypto, medical or dosage questions, or safety sizing such as beams, cables or lifting loads. Where a topic needs a value that only you can look up, the card says so and asks you to enter it. Read how the calculators work.

Who runs it

keepcalculator.com is an independent site. It carries no advertising and is not affiliated with any manufacturer, school or standards body. No card claims official status.

Get in touch

Found a wrong result, a typo or a formula that does not fit the title? Use the contact page or write to info@keepcalculator.com. Fixes are listed on the corrections page.