How to cut a recipe in half or double it

Find the multiplying factor

Every recipe adjustment starts with one number. The Institute of Child Nutrition, in its training lesson for child care meal programs, calls it the multiplying factor: the number of servings you need divided by the number of servings the original recipe makes. Its training example needs 35 servings from a recipe that yields 25, so the factor is 35 divided by 25, or 1.4.

The second step is to multiply each ingredient by that factor. In the same example, 3 cups of tomatoes times 1.4 gives 4.2 cups, which the Institute rounds up to 4¼ cups so it can be measured. The open textbook Basic Kitchen and Food Service Management, written by the BC Cook Articulation Committee, describes the same method as what you need divided by what you have, and adds a quick check: if you are making more, the factor is greater than 1, and if you are making less, it is smaller than 1.

At home the numbers are usually friendlier. A recipe that serves 4 becomes a meal for 2 with a factor of 0.5, for 6 with a factor of 1.5, and for 8 with a factor of 2. Write the factor at the top of the recipe before you start, then work down the ingredient list line by line.

Convert to smaller units before you divide

Halving a cup is easy. Halving 1/3 cup is where people stall. The fix is to restate the amount in a smaller unit that divides cleanly. The Institute of Child Nutrition's culinary measurement table gives the equivalents: 1 cup is 16 tablespoons, 1/3 cup is 5⅓ tablespoons, 1 tablespoon is 3 teaspoons, and 2/3 of a tablespoon is 2 teaspoons. Half of 1/3 cup is therefore 2⅔ tablespoons, which you measure as 2 tablespoons plus 2 teaspoons. Taste of Home's halving chart gives the same answer, and lists half of 3/4 cup as 6 tablespoons.

Mixed units need the same treatment. The Institute of Child Nutrition recommends converting amounts like 1 lb 8 oz into a single unit before multiplying, in that case 1.5 pounds, because the arithmetic is easier and more accurate. Halved, that is 0.75 pounds, or 12 ounces.

If you own a kitchen scale, weight makes all of this simpler. The National Institute of Standards and Technology calls measuring ingredients by mass a best practice for recipe accuracy, rather than measuring by volume with cups. The BC textbook goes further and advises expressing ingredients by weight before converting whenever possible, especially dry ones, while leaving very small amounts such as spices as volume measures. For reference, NIST lists 1 teaspoon as about 5 mL, 1 tablespoon as about 15 mL, 1 cup as about 240 mL, and 1 pound as 16 ounces or about 454 grams.

What to do with eggs

Eggs are the ingredient that refuses to divide. The American Egg Board notes that the large egg is the standard used in most recipe development, and that egg size matters most in baked goods. Its conversion chart puts about 5 large whole eggs in one cup, so a single large egg is a little over 3 tablespoons, and half of one is roughly 1½ tablespoons.

To halve an egg, Taste of Home suggests cracking it into a small dish, whisking it, and adding half, or weighing it on a scale and dividing the weight by two for precise baking. In a savory casserole the stakes are lower. Taste of Home's guide to converting a 13 by 9 inch recipe to an 8 by 8 pan says you can simply use the whole egg there, because an extra tablespoon or two of liquid makes little difference among about 8 cups of other ingredients, while a halved baking recipe should be weighed and split exactly.

Pans, cooking times and seasoning

Quantities scale neatly. Pans and ovens do not. Taste of Home gives the area of a 13 by 9 inch pan as 117 square inches, holding about 14 cups, and an 8 by 8 inch pan as 64 square inches, holding up to 8 cups. Because the halved recipe ends up at about the same depth in the smaller pan, Taste of Home says a halved casserole can go into the 8 by 8 without changing the oven temperature or the cooking time.

Doubling is less forgiving. In its guide to doubling baking recipes, Taste of Home points out that the more food there is in the oven, the longer it takes to bake. It advises against turning up the heat, which can overbake the outside while the inside is still raw. Start checking at the recipe's lowest suggested time and use the visual cues or the internal temperature the recipe gives. Check the equipment too: if a doubled dough is too much for your mixer, make two batches.

Seasoning is the other trap. The BC textbook warns that spices and seasonings must be increased with caution, because doubling or tripling them to match the factor can backfire, and recommends under-seasoning and adjusting just before serving. It also notes that cooking and mixing times can change whenever your equipment differs from the equipment the recipe was written for.

Common scaling mistakes

Scaling some ingredients and not others. Taste of Home's advice is to write the new amounts down before you start rather than trusting memory halfway through the bowl.

Scaling up a volume-only recipe a long way. The BC textbook notes that home recipes are usually written in volume measures, which are imprecise, and that increasing them dramatically magnifies the error. For big batches, convert to weights first.

Using the wrong measuring cup. NIST lists using a dry measuring cup for liquids, instead of a fluid measuring cup, as a common way to introduce measurement errors.

Swapping egg sizes without adjusting. The American Egg Board says that using a different size without an adjustment will affect texture, flavor balance and consistency in most recipes.

Redoing the math for the grocery list. Once a recipe is scaled, the shopping amounts change too. A meal planner like WeekPlate keeps a serving count on each planned meal, so a recipe that serves four can go on Thursday at two servings and the grocery list uses half of each of its ingredients.

Frequently asked questions