Everything in this category is arithmetic sitting on top of a number somebody else decided, and the decisions do not agree with each other. A "2 by 4" is a label, not a measurement: the American Softwood Lumber Standard says in as many words that a dry 2 by 4 is surfaced to 1 1/2 by 3 1/2 inches, and it also says board feet are counted on the nominal figure while cubic metres are counted on the dressed one — so the same plank has two honest volumes and you have to say which you meant. Stairs are worse, because the limits are law rather than convention and the law stops at a border: the International Residential Code allows a riser of 7 3/4 inches, Approved Document K allows 220 mm in an English house, OSHA allows 9.5 inches in an American workplace and the ADA Standards allow 7 inches on an escape route. The same 2.6 m floor-to-floor comes out at fourteen risers under one of those and eleven under another. Paint is the same shape of problem wearing a nicer label: one manufacturer prints 17 m² per litre and another prints 350 square feet per gallon, which is under 9 m² per litre, and neither of them is lying. So these tools name the document behind every figure, keep the ones that disagree apart instead of averaging them, and let you type the number off the thing in front of you over the top of all of it.
Tools in this category
Board foot calculator
Board feet and cubic metres from thickness, width, length and quantity, with the nominal-versus-actual trap named instead of quietly decided for you.
Stair calculator
Risers, riser height and tread depth from a total rise and the run you have, checked against the building document you pick rather than one country's limits.
Paint coverage calculator
Litres of paint for a room from wall sizes, coats and the spreading rate on your own tin, with doors and windows taken back off the total.
Suggest a tool
Tell us what is missing and where its numbers should come from.
What should it convert, calculate or generate, and where would the authoritative numbers come from? A link to the standard or publication that defines them is the most useful thing you can send.
Opens your mail app with this page already filled in.
How these tools are built
Every tool in this category runs entirely in your browser: there is no upload, no account and no request to a server once the page has loaded. The numbers behind them are transcribed from the organisation that defines them — NIST for units, the W3C for web formats, the WHO for health measures — and each page names its source next to the formula. A tool whose reference values stop reproducing fails the build and does not ship, which is the whole reason the catalogue grows slowly.