Scale a recipe to the number of people at the table

A recipe serves four. Six people are coming. The arithmetic is trivial and you'll still get it wrong somewhere around the third ingredient, because you're doing it in your head while also finding a pan.

What scales and what doesn't

The ingredient list scales cleanly. Almost nothing else does, and that's where doubling a recipe goes wrong.

Cooking time barely moves. Two chickens in an oven take a bit longer than one, not twice as long. A doubled stew simmers for about the same time. What actually changes is how long it takes to come up to temperature, not the cooking itself. Use the original time as a guide and check for doneness rather than trusting the clock.

Pan size matters more than you'd think. Double the ingredients into the same pan and you've doubled the depth. A tray of vegetables that roasted beautifully in one layer will steam in two. If you can't go wider, use two pans. This is the most common reason a doubled recipe tastes worse than the original.

Salt and spices go up less than the factor. Roughly, seasoning wants about three-quarters of what the arithmetic says when you double, and you correct upwards at the end. Chilli and strong spices especially. Under-seasoning is fixable at the table and over-seasoning isn't.

Raising agents need care. Baking powder and bicarbonate of soda don't scale linearly in large jumps. Doubling a cake is usually fine. Quadrupling it isn't, and the honest advice there is to bake two cakes.

Alcohol and acid reduce differently in a bigger pan, because there's more surface area relative to nothing much. Wine in a doubled sauce may need a little longer to cook off.

Halving is harder than doubling

Going down causes problems that going up doesn't.

• Eggs. Beat one, weigh it, use half. A medium egg is roughly 50 g out of the shell, so 25 g is your half-egg, and this works better than any rounding.
• Things that were already one. Half an onion, half a tin, half a stock cube. Fine, but the fridge fills up with halves.
• Pans that are now too big. A half batch spread thinly in the original tin will overcook at the edges. Go a size down.
• Braising liquid. Halving the liquid in a pan of the same width means it evaporates before the meat is done. Reduce the pan, not just the liquid.

How the numbers are rounded

Deliberately, and not the same way for everything.

Weights get whole numbers or halves, because that's what a scale can show and what your hands can act on. 266.67 g of flour is a true answer and a useless one. 267 g is what you weigh out.

Spoons get fractions instead of decimals. There's no such thing as a 0.67 teaspoon, but there is such a thing as two-thirds of one, and you can approximate that with the spoon already in your hand. So 1 tsp at 1.5× comes back as 1½ tsp, not 1.5 tsp.

Lines with no number are returned untouched. "A handful of basil" doesn't become "1.5 handfuls".

Doing this while you cook

This tool takes a list you paste in. It doesn't know your recipe, so it can't put the scaled amounts back where you'll be reading them, which is the part that matters when your hands are covered in flour.

In Fork & Spoon the servings control lives on the recipe itself. Change the number of people and every amount follows, in the step-by-step cooking mode as well as the list. Send that to the shopping list and it goes in at the scaled amounts, grouped by supermarket aisle.

If you also need to move between cups and grams, the cups to grams converter here handles the per-ingredient part, which matters more than most converters admit.