Recipe Scaler

Scaling a recipe, step by step

Every scaled recipe starts with one number: the factor. Divide the servings you want by the servings the recipe makes. A recipe for 4 that has to feed 6 gives 6 ÷ 4 = 1.5, so every quantity is multiplied by 1.5. Halving is the same arithmetic in reverse — 2 ÷ 4 = 0.5. The hard part was never the multiplication; it is that kitchens do not own a 0.75 teaspoon, so the answer has to come back as a fraction you can actually measure.

Worked example: 4 servings to 6

Take the shopping list this tool starts with: 2 cups flour, 1/2 tsp salt, 3 tbsp butter, 1 egg. At a factor of 1.5 the flour becomes 3 cups, the salt becomes 3/4 tsp, the butter becomes 4 1/2 tbsp, and the egg becomes 1 1/2. Three of those are easy. The half egg is the one everybody gets stuck on: crack two eggs, beat the second one smooth, and add half of it by weight — a large US egg is about 50 g without the shell, so half is 25 g, or roughly 1 1/2 tablespoons. The tool flags that line for you rather than pretending 1.5 eggs is a normal instruction.

The salt deserves a second look too. Multiplied out it reads 3/4 tsp, but seasoning is the one ingredient most cooks should hold back on when scaling up. Start at about 75% of the scaled figure — a scant 1/2 teaspoon here — cook, taste, and add the rest at the end. You can always put salt in; you cannot take it out.

Worked example: halving a tray bake

A tray bake for 12 that you want for 5 gives a factor of 5 ÷ 12 = 0.417. A cup of sugar becomes 0.417 cups, which the tool rounds to the nearest usable measure: 3/8 cup, or 6 tablespoons if your set stops at quarters. 350 g flour becomes 146 g — and this is where a scale earns its price, because 0.417 of a cup measured by scooping is a coin toss. Two teaspoons of baking powder become a shade under 1 teaspoon, which is fine; leavening only misbehaves in the other direction.

What does not scale in a straight line

Cooking time is the rule people break most often. Doubling a beef stew does not double two hours into four. The pot is wider, the heat still has to travel through the same depth of liquid, and the extra mass mostly costs you a longer come-up to a simmer — usually 10 to 20 minutes more, then the same braise. Roasts are the exception worth knowing: two chickens in one oven take a bit longer than one, because the oven has to reheat more mass, but nothing like twice as long.

Pan maths: match the area

Cake tins are labelled by diameter and filled by area, which is why a "one inch bigger" tin swallows a batter that used to fill it. Area of a round tin is pi times the radius squared. An 8-inch round is 3.14 x 4² = 50.3 square inches; a 9-inch round is 3.14 x 4.5² = 63.6. The ratio is 63.6 ÷ 50.3 = 1.27, so going from an 8-inch to a 9-inch tin means scaling the recipe by about 1.27 to keep the same depth — or accepting a flatter, faster-baking cake if you do not.

Rectangular tins are easier: length times width. An 8x8 is 64 square inches, a 9x13 is 117, so the bigger tin takes about 1.8 times the batter. Two 8-inch rounds equal roughly one 9x13 (100.5 vs 117 square inches, close enough for most bakes). Whatever the shape, keep the batter depth between about half and two-thirds of the tin height, and add 5 to 15 minutes if the scaled batter sits deeper than the original.

Weigh it if you are scaling up

Volume measures have a tolerance that compounds. A cup of flour is anywhere from 120 g to 150 g depending on whether it was scooped or spooned, so a recipe tripled by cup ends up somewhere in a 90 g range — the difference between a tender crumb and a brick. Grams do not have that problem. If you plan to scale often, switch to a digital scale for flour, sugar and butter and leave the cups for liquids. It is the single change that makes a scaled bake behave like the original.

Limits of this tool

It reads a number at the start of each line and multiplies it. Lines with no leading quantity — section headings, "salt to taste", "a splash of oil" — are passed through untouched and marked, so nothing quietly vanishes from your list. For teaspoons, tablespoons and cups it adds the easier equivalent next to the result — 12 tbsp is also shown as 3/4 cup, and 1/8 cup as 2 tbsp — but it leaves grams, millilitres and ounces alone. It does not adjust anything for altitude, pan material or convection ovens, and it cannot tell you whether your mixer can handle the bowl volume you are about to demand of it. For everything the arithmetic cannot see, the table above is the checklist.