Recipe scaler

Scale a recipe

One quantity per line, with the number first — for example `200 g flour`. Lines with no number are passed through unchanged.

What does not scale

Ingredients scale. Almost nothing else does, and this is where doubled recipes go wrong.

Cooking time does not scale. Doubling a stew does not double the cooking time, because the pot is not twice as deep in every direction. It usually adds a modest amount. Doubling a cake into two tins keeps roughly the same time; doubling it into one deeper tin adds a great deal.

Pan size does not scale linearly. Twice the mixture in the same tin is twice as deep, which changes how heat reaches the middle. Either use two tins or accept a longer, lower bake.

Salt and strong seasonings scale imperfectly. Doubling chilli, salt and spice usually overshoots. Scale them to about three-quarters and adjust by tasting.

Raising agents scale down badly. Halving a cake and halving the baking powder works; halving an egg does not.

Liquid in a wider pan evaporates faster, so a doubled sauce in a bigger pan may reduce more than you expect.

Practical advice

• Weigh, do not measure by volume, especially when scaling. Errors multiply.
• Round sensibly. 1.33 eggs is not a quantity. Round to a whole egg and adjust the liquid slightly, or scale to a factor that gives whole eggs.
• Scale by weight where you can. Scaling "1 onion" is guesswork; scaling "150 g onion" is not.
• Do not scale a recipe up more than about three times in one pot. Browning, evaporation and heat transfer all change, and the result is a different dish.
• Taste more often when scaling up. The seasoning will not be where the arithmetic says.
• For baking, scale to whole eggs. Work out the factor that gives you a whole number of eggs and use that.

Why a doubled recipe is not twice a recipe

Scaling ingredients is arithmetic. Scaling the cooking is not, because most of what happens in a pan or an oven depends on surface area and depth rather than on total quantity.

Double the contents of a casserole and you roughly double the volume — but the surface exposed to the heat grows much less than that, and the distance from the outside to the middle grows. So heat takes longer to reach the centre, and evaporation, which happens only at the surface, accounts for a smaller share of the liquid. A doubled stew is wetter and slower than the arithmetic suggests.

The same logic explains browning. Twice the meat in the same pan is a crowded pan, the released steam has nowhere to go, and nothing browns. The fix is not more heat but more pan: brown in two batches, or use two tins, and the scaling works.

And a doubled cake in one deeper tin is the clearest case of all. The mixture is twice as deep, so the outside sets and browns long before the centre is cooked. Two tins of the original depth behave almost exactly like the original recipe; one deep tin does not.

Common questions