The Simple Part: What Scales Linearly
Most structural ingredients scale in direct proportion. If you double a recipe, you double these:
- Flour — double the recipe, double the flour. 250g becomes 500g.
- Sugar — same linear scaling. 200g becomes 400g.
- Butter and oils — double them. 113g butter becomes 227g.
- Eggs — double them. 2 eggs become 4 eggs. (If halving and you need "half an egg," beat one egg and use half the volume — about 25g.)
- Milk, cream, and other liquids — linear.
- Chocolate, nuts, dried fruit — linear.
For these ingredients, the math is straightforward. Multiply every amount by your scaling factor and move on.
The Tricky Part: What Doesn't Scale Linearly
Baking Powder and Baking Soda
Chemical leaveners don't scale perfectly. If you double a recipe, use about 1.5 to 1.75 times the baking powder instead of double. Too much baking powder gives a bitter, metallic taste and can cause the batter to rise too fast then collapse. A recipe calling for 2 teaspoons of baking powder should get about 3 to 3.5 teaspoons when doubled, not 4.
Baking soda follows the same principle, but it's also tied to the amount of acid in the recipe (buttermilk, yogurt, lemon juice, brown sugar). If you're scaling up, make sure the acid scales proportionally.
Yeast
When doubling a bread recipe, use about 1.5 times the yeast, not double. The extra yeast produces more gas than the dough can contain, leading to over-proofing and a coarse, yeasty-tasting bread. If tripling a recipe, you might only need 2 times the yeast. The yeast colonies grow exponentially — they don't need a linear increase to do their job.
Salt
Salt is potent. When doubling, use about 1.75 times the salt, then taste if possible (for doughs where you can taste the raw batter or dough safely). You can always add more later; you can't take it away. When halving a recipe, use slightly more than half — salt has a threshold below which food tastes flat.
Spices and Extracts
Scale these to about 1.5 times when doubling. Strong flavors like vanilla, cinnamon, and nutmeg become overpowering if you double them exactly. Start with 1.5x and adjust to taste.
Baker's Percentages
Professional bakers use a system called baker's percentages (also known as baker's math). Every ingredient is expressed as a percentage of the flour weight. Flour is always 100%.
For example, a basic bread recipe:
- Flour: 500g (100%)
- Water: 350g (70%)
- Salt: 10g (2%)
- Yeast: 5g (1%)
To scale this to any amount, decide how much flour you want, then calculate everything else as a percentage. Want 750g of flour? Water = 750 x 0.70 = 525g. Salt = 750 x 0.02 = 15g. Yeast = 750 x 0.01 = 7.5g.
Baker's percentages make scaling painless and also let you compare recipes easily. A bread with 65% hydration will behave very differently from one with 80% hydration, and you can see that at a glance from the percentages.
Pan Size Matters
Scaling a recipe doesn't just mean scaling the ingredients — you need the right pan size too. Doubling a cake recipe means you need a pan with roughly twice the volume. A 20cm (8-inch) round pan holds about 6 cups of batter. A 23cm (9-inch) round pan holds about 8 cups. So if you double a recipe for a 20cm pan, you'd need two 20cm pans or one 23cm pan plus a small extra pan.
Alternatively, if you're doubling a recipe and using a larger pan, the thicker batter layer means a longer bake time. Add 10-15 minutes and start checking early. The center takes longer to reach temperature when there's more batter above and below it.
Practical Tips
- Always scale by weight, not volume. "Double 1 cup of flour" introduces measuring error twice. "Double 125g of flour to 250g" is exact.
- Write out the full scaled recipe before you start. Don't try to do the math while you bake.
- When halving, watch your pan size. A half-batch in a full-size pan will spread too thin and overbake.
- Test one batch at the original size first, then scale. Scaling a recipe you've never made is asking for trouble.