The single most useful kitchen math is scaling a recipe to the number of people you're actually feeding. It's one division and a lot of multiplication — and with the right approach it works for almost any dish.
The one formula that matters
Scale factor = new servings ÷ original servings. Apply it to every ingredient and the recipe will keep its proportions. This is the difference between cooking for two with a recipe built for six, and accidentally cooking for twelve.
What to scale exactly, what to fudge
Flour, liquids and protein scale precisely. Salt, spice and leavening usually want a slightly softer touch — they compound, and rounding errors become flavour errors. Taste-testing remains the ultimate check.
Beyond the numbers
Pan size, heat and timing don't multiply by the same factor. A smaller batch in the same pan cooks faster; a bigger one needs gentler heat. The scale factor handles quantities; judgement handles the rest.
Frequently asked questions
Divide the new number of servings by the original to get a factor, then multiply each ingredient by it. 4 servings to 6 is a 1.5× factor.
Approximately, but seasonings are forgiving — scale them a little less and taste, since doubling a spice can quickly overpower a dish.
Yeast and leavening in breads, and cooking time. A doubled recipe doesn't need double the time — it often needs only a bit more.