How to halve or double a recipe

A recipe for four must feed ten on Sunday, or a cake recipe for a large tin must fit the small one you own. Scaling looks like plain multiplication, and for most ingredients it is. The mistakes come from the few things that do not scale in a straight line: seasoning, raising agents, pan size and time.

Step 1: find the factor

Divide what you want by what the recipe makes. The recipe serves 4 and you need 10: the factor is 10 ÷ 4 = 2.5. You want half: the factor is 0.5. Write the factor at the top of the recipe, then multiply every ingredient by it and write the new amounts down before you start. Scaling in your head while cooking is how one ingredient gets forgotten.

Step 2: tame the awkward amounts

Halving and thirding produce amounts no spoon measures. These equivalents help:

Amount	Half	One third	Double
1 tablespoon	1 1/2 teaspoons	1 teaspoon	2 tablespoons
1/4 cup	2 tablespoons	4 teaspoons	1/2 cup
1/3 cup	2 tablespoons + 2 teaspoons	1 tablespoon + 2 1/3 teaspoons	2/3 cup
1/2 cup	1/4 cup	2 tablespoons + 2 teaspoons	1 cup
2/3 cup	1/3 cup	3 tablespoons + 1 2/3 teaspoons	1 1/3 cups
3/4 cup	6 tablespoons	1/4 cup	1 1/2 cups
1 cup	1/2 cup	1/3 cup	2 cups
1 teaspoon	1/2 teaspoon	a generous 1/4 teaspoon	2 teaspoons

Converting to a smaller unit first makes any amount easy. A third of a quarter cup is hard to picture, but a quarter cup is 12 teaspoons, and a third of that is 4 teaspoons.

Half an egg

Beat the egg in a cup, then use half. A beaten medium egg is about three tablespoons, so half is one and a half tablespoons. The other half goes into tomorrow's omelette.

Step 3: know what not to multiply straight

Salt, chilli and strong spices. When doubling or more, start with about three-quarters of the multiplied amount, taste near the end and adjust. A larger pot loses less to evaporation, so the seasoning concentrates less.
Whole spices in tadka. A doubled dal does not need double the cloves, cardamom or bay leaf. Go to one and a half times.
Oil for frying and tadka. Oil depends on the surface of the pan more than on the quantity of food. Double the food rarely needs double the oil.
Water in dal, curry and rice. A wide, full pot boils away proportionally less water. Add four-fifths of the multiplied water first and top up if needed. For rice in a pressure cooker, keep to your usual ratio.
Baking powder and baking soda. Fine to multiply for double or half. Beyond that, bake two batches instead of one giant one.
Yeast. Multiplied yeast works, but a large dough rises faster in the middle because it holds its warmth. Watch the dough, not the clock.

Step 4: the pan and the time

Cooking time does not double when the recipe doubles. It depends on thickness, not on total amount.

On the stove: a doubled curry takes longer to come to the boil, then simmers for about the same time. Onions take longer to brown in a crowded pan, so use a wider pan or brown in two batches.
In a pressure cooker: never fill above the maker's line (usually half full for dals, which froth, and two-thirds for other foods). Cooking time after the first whistle stays about the same. If the doubled recipe does not fit, cook twice.
In the oven: a deeper cake needs a lower temperature and a longer time, and a shallower one the reverse. The safest way to double a cake is to bake it in two tins of the original size. To move to a different tin, use the cake tin size chart.
Deep frying: fry in the same small batches as before. More pieces at once cool the oil, and the food turns greasy.

Scaling down

Halving works well for almost everything. Below half, small errors grow: a quarter of a teaspoon of baking soda measured slightly wrong is a large mistake. For very small batches, measure spoon amounts with extra care, use a smaller pan so the food is not spread too thin, and begin checking well before the stated time.

Cooking for a crowd

For a function, do not scale a family recipe by ten. Quantities per person behave differently at that size, and many dishes share each plate. Our how much to cook per person calculator gives rice, dal, atta and vegetable quantities for any number of people.

Write it down

When a scaled recipe turns out well, note the amounts you actually used, the pan and the time. The next time is then a recipe, not an experiment.

Questions people ask

How do I halve one egg?

Beat it lightly and use half: about one and a half tablespoons of a medium egg.

Do I double the cooking time when I double a recipe?

No. Time depends on how thick the food is, not on the total amount. A doubled curry simmers for about as long; a deeper cake needs longer at a slightly lower heat.

Should I double the salt when I double a recipe?

Start with about three-quarters of the doubled amount, taste towards the end and add more if needed.

What is half of three-quarters of a cup?

Six tablespoons.