Recipe Scaler
Rescale a whole recipe at once, with the ingredients that should not scale linearly flagged.
In short
To scale a recipe, multiply every ingredient by the new servings divided by the original servings. Most ingredients scale linearly, but leavening agents, salt, spices and baking times do not: doubling a cake does not mean doubling the baking powder or the time in the oven.
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What scales and what does not
Most ingredients scale linearly. Flour, sugar, butter, liquid, fruit, meat and vegetables all just multiply. Three things do not.
Leavening
Baking powder, bicarbonate of soda and yeast produce gas relative to the structure of the batter rather than simply its mass. Double them and a cake rises too fast, outruns its own structure and sinks in the middle. There is often a metallic aftertaste too.
A workable rule when doubling: use about 1.5 times the leavening, not twice. When halving, use slightly more than half.
Salt and strong spices
Perception of salt, chilli, cloves, cinnamon and anything assertive is not proportional to quantity. Doubling a curry and doubling the chilli usually produces something noticeably hotter than the original rather than the same dish twice.
Scale to about 1.5 times when doubling, taste, and adjust upward. You can always add more; you cannot take it out.
Cooking time
This is the one that ruins things. Heat reaches the middle of a dish at a rate governed by its depth, not its total volume. A cake twice the size in the same tin is twice as deep and takes far longer than twice as long. Spread across two tins it takes almost the same time as the original.
Practical approach: keep the temperature, start checking early, and expect roughly a third more time for a doubled quantity in a deeper tin. For anything deep, drop the oven 10 to 15 degrees so the outside does not overcook before the centre sets.
Scaling by tin size
Tins are compared by area, not diameter, and this catches people out constantly because area rises with the square of the radius.
| From | To | Multiply by |
|---|---|---|
| 20 cm round | 23 cm round | 1.32 |
| 20 cm round | 25 cm round | 1.56 |
| 23 cm round | 20 cm round | 0.76 |
| 20 cm round | 20 cm square | 1.27 |
| 20 cm square | 23 cm square | 1.32 |
A 23 cm tin holds about 40% more than a 20 cm one despite being only 15% wider. Pouring a 20 cm recipe into a 23 cm tin gives you a thin, dry, overcooked cake.
Weigh, especially when scaling
Scaling exposes the weakness of volume measures. Two thirds of three quarters of a cup is not a measurement anyone can execute. In grams it is a multiplication.
Grams also scale honestly. A scaled cup measure inherits all the compaction error of the original and then multiplies it. The cooking converter handles cups to grams per ingredient, since a cup of flour and a cup of honey are very different weights.
Things that do not scale at all
- Pan size for frying. Doubling meat in the same pan steams it instead of browning it. Cook in batches.
- Marinating and resting times. These depend on thickness, not quantity.
- Reduction. A sauce reducing in a wider pan behaves differently. Judge by consistency, not the clock.
- Yeast doughs. Proving time depends on temperature and yeast activity, not batch size.
- Egg-based emulsions. Mayonnaise and hollandaise get harder to hold together at larger volumes.
A note on halving eggs
The recurring problem with halving. Beat one egg thoroughly, weigh it, and use half by weight. A medium egg is roughly 50 g out of shell, so 25 g is a half. Guessing by eye matters more in baking than in most cooking, since eggs provide structure as well as moisture.
Frequently asked questions
How do I double a recipe?
Multiply every ingredient by two, with three exceptions: leavening agents, salt and strong spices, and the cooking time. Doubling baking powder gives a cake that rises then collapses, and doubling the time burns it.
Why do some ingredients not scale?
Because their effect is not proportional to the quantity. Leavening produces gas relative to the surface area and structure of the batter, not just its mass. Salt and strong spices are perceived non-linearly. And heat reaches the middle of a larger dish more slowly, so time scales with depth rather than volume.
How do I adjust the baking time?
Keep the temperature and check considerably earlier than the scaled time suggests. A rough guide is that doubling the quantity adds about a third to the time, not double. For anything deep, drop the oven 10 to 15 degrees so the outside does not overcook before the middle sets.
Can I scale a recipe by tin size?
Yes, and it is more reliable than guessing. Scale by the area of a round or square tin rather than its diameter, because area rises with the square of the radius. A 23 cm tin holds about 40% more than a 20 cm tin, not 15%.
Is it better to weigh?
Yes, particularly when scaling. Scaled cup measures produce awkward quantities like two thirds of three quarters of a cup, whereas grams multiply cleanly. The cooking converter handles cups to grams per ingredient.