You found the perfect banana bread recipe for 8 servings, but you need to feed 12. Or the chocolate cake makes too much for two people. Scaling looks like simple arithmetic — multiply every ingredient by 1.5 — and for most recipes, that is genuinely most of the answer. The rest is knowing which ingredients resist arithmetic, and how time and temperature actually behave.
The 80/20 rule of scaling
For cakes, cookies, muffins, quick breads and most pastries, scaling between 0.5× and 2× is essentially safe: multiply every ingredient by the same factor, keep the same method, keep the same oven temperature. The recipe was probably tested at its base size and remains forgiving across that range. Where it gets interesting is above 2× (or below 0.5×), with eggs, with leaveners, and with bake time.
Our recipe scaler multiplies every line of your ingredient list at once — paste, set servings, and get fractions instead of decimals. It handles ½, ¾, 1½ and 2/3 inputs, keeps unit notes intact, and leaves unparseable lines untouched so you never lose context.
Eggs: the rounding problem
Recipes say "2 eggs" because eggs come in whole units. Scale a 2-egg recipe by 1.5 and you need 3 — fine. Scale by 1.25 and you need 2.5 eggs, which is where bakers improvise: use 2 eggs plus 1 tablespoon of beaten egg white (or weigh: a large egg's contents weigh about 50 g, so 25 g of beaten egg equals half an egg). For very large scalings, weigh your eggs and multiply — a bowl of beaten egg scaled to 375 g is exactly what a 7.5× recipe needs.
When a recipe uses eggs as its only leavening support — think genoise or chiffon — weighing becomes non-negotiable, because the egg volume is the structure. If your doubled recipe needs "5.6 eggs", weigh: 280 g of beaten egg.
Leaveners: less than proportional
Baking powder and baking soda do not always scale linearly. Doubling a recipe usually works with double the leavener because you are also doubling the batter's acidity and moisture that activate it. But at 3× and beyond, many bakers hold leavener at 2.5–2.8× the original rather than 3×: a slightly taller, more stable rise, and no metallic baking-soda taste from the extra neutralisation products.
Salt, by contrast, can usually be scaled proportionally without trouble; taste is subjective, so keep it simple.
Bake time does not scale linearly
This is the mistake that ruins scaled bakes. A doubled cake does not take twice as long — the batter is thicker only slightly, and heat still penetrates from all sides. In practice, doubling a 30-minute cake recipe usually needs 35–40 minutes, not 60. Halving a 60-minute loaf needs about 45 minutes, not 30.
The reliable method: keep the temperature identical, start checking at the original recipe's time minus 10 minutes, and test with a skewer or a thermometer (cakes are done around 93–96 °C in the centre; breads around 96–99 °C). Write down the real time in the margin for next time — after two runs you will know your pan and oven exactly.
Scaling between pan sizes
Changing pan size while keeping the same servings is a different scaling problem: you are changing the surface area, so you need an area ratio, not a serving ratio. A 23 cm round has an area of about 415 cm²; a 9×13 in rectangle about 759 cm². The rectangle needs × 1.83 of the batter — and because the batter is thinner, it bakes faster. See the pan size guide and use the pan converter for any shape pair.
What about flavourings and spices?
Vanilla, cinnamon, nutmeg and salt are the ingredients bakers adjust by taste rather than arithmetic. When doubling a recipe that calls for 1 tsp vanilla, use 1½–2 tsp — vanilla is subtle and rounding down is kinder than rounding up. Spices like cloves and cardamom are intense: scale them proportionally at first, taste the batter, and adjust. You cannot un-add a teaspoon of cloves.
Scaling down: watch the equipment
Halving works beautifully until you hit equipment limits. A mixer that handles a 6-egg batter may barely cream 2 eggs and 100 g of butter — the paddle needs enough mass to work. When scaling below 0.5×, switch to a bowl and whisk for creaming, or keep the mixer running longer at low speed. Small batches also bake faster: a single muffin is done noticeably sooner than a pan of twelve.
The workflow that never fails
Write the original recipe down. Choose the factor. Scale every ingredient by weight (volume for eggs and liquids is fine). Keep the method and temperature. Reduce nothing, increase nothing — except your attentiveness near the end of the bake. That routine, repeated, teaches you more about your own oven than any recipe book. And when the list is long, let the scaler carry the arithmetic while you carry the whisk.