Recipe Scaler

Scaling a recipe is multiplication, and the arithmetic is the easy part. The hard part is knowing which lines the multiplier is wrong for — because several of them are, and a recipe scaled straight down the list is how a doubled cake comes out bitter and a doubled braise comes out watery. This tool does the arithmetic on every line and leaves the judgement to you; what follows is the judgement.

How the parsing works

Each line is read for a leading quantity — whole numbers, fractions like 1/2, mixed numbers like 1 1/2, unicode fractions like ½ and ⅓, decimals, and ranges like 2-3. That number is multiplied by the ratio of desired to original servings and converted back to the nearest common kitchen fraction. Lines with no leading number pass through untouched, which is deliberate: "salt to taste" and "a splash of vinegar" are instructions to your palate, not quantities, and multiplying them would be meaningless.

Where it helps, the quantity is re-expressed in a more sensible unit — and "sensible" means the drawer rather than the arithmetic. Tripling 1 tsp salt gives 1 tbsp salt rather than "3 tsp", and doubling 1/4 cup butter gives ½ cup rather than the identical "8 tbsp", because that is one scoop instead of eight. It will not hand you part of a tablespoon: halving 1 tbsp comes back as 1½ tsp, because a measuring set has ¼ and ½ teaspoons in it and nothing smaller than a whole tablespoon. Three teaspoons to a tablespoon, sixteen tablespoons to a cup.

The four things that don't scale linearly

Salt, when it is seasoning. Whether salt scales depends entirely on what it is doing. In bread dough it is structural — it controls fermentation and gluten, bakers set it at 1.8–2% of flour weight, and it scales exactly. In a brine or a cure it is doing chemistry against a mass of meat, and it scales exactly there too. But salt added to season a finished dish scales sub-linearly, because perceived saltiness rises more slowly than concentration. Doubling a soup, start at about 1.5× the salt, taste at the end, and correct. Under-salting is fixable at the table; over-salting is not fixable at all.

Chemical leavening. Baking powder and baking soda produce their gas on a schedule, but a bigger batter takes longer to set. Scale them fully and the structure rises before it can hold, then falls — a domed, cracked top over a sunken middle, and a soapy or metallic edge from the unreacted soda. The working rule is about 1.75× for a doubled batch and about 2.5× for a tripled one. Yeast is the opposite problem and is usually left near 1× when scaling up: it multiplies on its own, and a bigger dough holds its heat better, so a fully scaled yeast quantity ferments faster than you expect rather than slower.

Anything that reduces. Evaporation happens at the surface, not through the volume, and this is the one that surprises people. Double a braise and cook it in the same pot, and you have doubled the liquid while barely changing the area it can leave from — so the sauce that took 40 minutes to tighten now never gets there, and the meat overcooks while you wait for it. Two fixes, and you want both: hold the liquid back to roughly 1.5× rather than 2×, and move to a wider pan so the surface scales with the volume. The same logic runs in reverse when you halve a recipe in the pan you always use — it will reduce far too fast.

Strong aromatics. Chile, garlic, bay, clove, rosemary and anything smoked compound in a way that mild ingredients don't. Start at 1.5× for a doubled batch and taste before adding the rest. These are also the ingredients that keep developing after the pot comes off the heat, so a dish that is correct at serving time is often too aggressive as leftovers.

Eggs, and the halving problem

Eggs are the most common reason a scaled recipe can't be executed as written. Halving a three-egg cake gives 1½ eggs, which is a real quantity and not a usable instruction. Weigh instead: out of the shell a large egg is about 50 g, of which roughly 18 g is yolk and 32 g is white. Beat one egg thoroughly and weigh out half. When the recipe leans on eggs for richness rather than lift, two yolks in place of one whole egg is the usual substitution; when it leans on them for structure — a sponge, a meringue, a custard — weigh it properly, because yolk and white do opposite jobs and swapping the ratio changes the result more than the quantity does.

Pan size, and why bake time barely moves

Pans scale by area, not by their headline dimension. A 9-inch round is π × 4.5² ≈ 63.6 sq in; a 9 × 13 is 117 sq in; so moving between them is a factor of about 1.84, not 2. But the more useful number is depth, and it is the one nobody checks. If you scale a batter by 1.84 and pour it into 1.84× the area, the depth is unchanged and the bake time is nearly unchanged. If you pour a doubled batter into the same pan, you have doubled the depth, and the bake time goes up by far more than the volume did — the outside is done long before the middle.

So: keep the depth constant and the time roughly constant. Where you can't, leave the oven temperature alone — dropping it 25°F is sometimes suggested for a deep cake, but the reliable move is to go by an internal temperature or a visual cue rather than the clock. Most cakes are done at 205–210°F in the centre; a custard sets around 175–180°F; bread is 195–210°F depending on style. A scaled recipe's stated time is the first thing to stop trusting.

The things that don't come out of the pan at all

Browning is a surface phenomenon too. Doubling a sauté and putting it all in the same pan drops the pan temperature, releases moisture faster than it can boil off, and steams the food grey instead of browning it. Cook in two batches, or move up a pan size. This costs time the scaled recipe doesn't mention and is the single most common reason a doubled dish tastes flat.

Weigh, don't scale volumes, when precision matters. Cup measures carry maybe 10–20% error depending on how the flour was packed, and scaling multiplies that error along with the quantity. Past about 2×, converting to weight first is worth more than any of the adjustments above. Check your equipment while you are at it — a mixer or pot that is comfortable at 1× may not hold 3×.

Worked examples

• Doubling a flavouring. 3 tsp vanilla extract × 2 → 2 tbsp vanilla extract. Extract is not a compounding aromatic, so the full multiplier is right here.
• A seasoning at 1.5×. 1/2 tsp salt × 1.5 → ¾ tsp salt, which is the half and the quarter spoon together rather than the equivalent quarter-tablespoon nobody owns. Seasoning salt is also the line to hold back and correct at the end.
• A range stays a range. 2-3 cloves garlic × 2 → 4-6 cloves garlic. Garlic is compounding, so take the bottom of that range and taste up.
• Halving eggs. 3 eggs × 0.5 → 1½ eggs — the arithmetic is right and the instruction is not. Beat two eggs (100 g), use 75 g.
• A 4-serving pancake batter to 6. 1 cup flour → 1½ cup flour, 1 1/2 cups milk → 2¼ cups milk, 3 tsp baking powder → 1½ tbsp. At 1.5× the leavening correction is small enough to ignore; at 2× take about 1.75×, and at 3× about 2.5×.