Recipe scaling calculator
Scale a recipe up or down. Multiplying the ingredients is the easy part — the useful half is what does not multiply. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
What does not scale
Multiplying the ingredients is the easy part, and every scaler on the internet stops there. The things that go wrong are the things that do not multiply:
Cooking time, above all
Double a cake and it does not take twice as long. Heat travels inward from the surface, so the time depends roughly on how deep the thing is, not how much of it there is. Double the recipe into a tin of twice the area and the depth barely changes — so does the time. Double it into the same tin and the depth doubles, and the time goes up by much more than you expect while the outside burns.
Keep the temperature where the recipe put it, and start checking at the original time.
The tin scales by area, not by width
Double the mixture needs double the area, which is about 1.4 times the width — the square root of two. Going from an 8-inch round to a 16-inch round is not twice the tin, it is four times. The baking tin calculator does that sum.
Eggs, and other things that come in units
Two eggs times one and a half is three, which is fine. Two eggs times 1.2 is 2.4, which is not. Beat the eggs together and weigh out the fraction — a medium egg is about 50 g out of the shell, roughly two-thirds white and one-third yolk. The same goes for tins of tomatoes and packets of yeast: round the pan, not the chemistry. Flour, sugar, fat and liquid have to keep their ratios or the recipe stops working; one extra mushroom does not matter.
Salt and spice
These scale arithmetically and then need tasting anyway. Strong flavours are judged against the whole dish rather than measured, and a recipe developed for four has usually had its seasoning nudged to taste at the end. Scale it, then taste it.
What it will not do
- It will not understand your ingredients. It finds a number at the start of each line and multiplies it; the words are left exactly as you typed them.
- It will not convert units on the way past. That is the cooking converter, deliberately kept separate — silently reinterpreting “1 cup” as 240 ml when your recipe meant 236.59 is the kind of help nobody asked for.
- It will not handle fractions written as words. “Half a teaspoon” is left alone; “1/2 tsp” is scaled.