About The Pocket Reckoner
A reckoner is a pocket book of ready calculations. The Pocket Reckoner is that book, online: 927 free calculators for the questions people actually ask — taxes and household money, health and fitness, building and home projects, cooking, school, work, travel and more.
Each calculator shows its formula, works one example by hand and names its sources — the IRS, CDC, NIST, OpenStax and similar primary references. Where two good sources disagree, we show both and say which one we used.
How the building calculators work
- Volumes are plain geometry: length × width × depth, converted to cubic feet, cubic yards or cubic metres.
- Bag counts use the yields manufacturers publish for their bags — for example, about 0.60 cubic feet for an 80 lb bag of concrete mix. If your bag lists a different yield, go by your bag.
- Prices are yours. Nothing is pre-filled, because prices change from store to store and week to week.
- Every result includes a waste allowance you can see and change, because running short in the middle of a job costs more than a few extra bags.
What they are not
The calculators do the arithmetic, not the engineering. For footings, retaining walls or anything structural, check your local building code and talk to a qualified professional.
Everything else
The other sections — money and tax, health, dates and time, math and statistics, science, tech, food and everyday life — follow the same rules: the formula is on the page, the examples are worked out by hand and checked by automated tests, and nothing is sent anywhere — every calculation runs in your browser. How each one is checked before it goes live is onHow we check our calculators.
Who makes it
The Pocket Reckoner is made by Buyan LLC. Found a mistake, or need a calculator we don't have yet? Tell us on the Contact page.