The arithmetic in this category is the easiest on the site and the numbers behind it are the least settled, which is the whole reason the pages exist. Scaling a recipe is one multiplication, but the multiplication is the part that always works; what goes wrong is everything the factor does not touch — the pan, the bake, the seasoning. Feeding a crowd has no exact answer at all, only figures that extension services publish because somebody has to start somewhere, and they are appetites rather than measurements. So these tools do two things. They do the arithmetic exactly, and they say out loud which of their numbers is a definition, which is a transcribed guideline, and where the guideline stops covering the situation you are in. A page that quietly turned a rule of thumb into a decimal would be more confident than its own source, and that is the one failure mode worth designing against here.
Tools in this category
Recipe scaler
Rewrite a recipe for a different number of servings, and see which of its lines the multiplying factor is the wrong tool for.
Bill splitter
Split a bill with the tip added, evenly or with one person covering a stated share of it, and see the tip and the grand total alongside.
Party food quantities calculator
How much food and drink a party needs, worked from the per-guest figures an extension service publishes rather than from a number we made up.
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.