You've got a recipe for four and six people coming. Or a treasured formula for a dozen cookies and a bake sale to fill. Scaling seems like simple multiplication — and for most ingredients it is — but a few quietly refuse to follow the rule, and knowing which ones separates a good result from a salty, over-leavened one.
Start with the scaling factor
The scaling factor is desired yield divided by original yield. A recipe for 4 that you want to serve 6 has a factor of 1.5. Multiply each ingredient by that factor and you have your baseline. Working from weights rather than cups makes this far more accurate — 1.5× of 200 g is unambiguous in a way that 1.5 cups-and-a-half is not.
- Scaling factor = new servings ÷ original servings.
- Multiply every ingredient weight by that factor for a first pass.
- Convert awkward results to sensible units: 1.5 eggs becomes 'beat 2 eggs and use three-quarters'.
Recipe Scaling Calculator
Enter the original and target servings to rescale every ingredient at once.
The ingredients that don't scale linearly
Season and leaven by taste, not by multiplication
Salt, spices, leavening (baking soda/powder) and alcohol don't scale cleanly. Multiply them by about 75–90% of the factor, then adjust at the end. Tripling the chilli or the baking powder is how scaled-up dishes go wrong.
The reason is that these ingredients act on the food non-proportionally — a little salt seasons a lot of volume, and leavening reacts with surface area and time, not just quantity. Scale them conservatively and correct upward if needed.
Pans, heat and time
Volume scales with the cube of size, but surface area scales with the square — so a bigger cake bakes differently, not just longer. Keep the batter depth similar by choosing a larger pan rather than a taller fill, keep the oven temperature the same, and start checking for doneness at the original time. Judge by internal temperature or a skewer, never by the clock alone.
Scale the bulk ingredients by ratio, hold back on the seasonings and leaveners, and let your senses make the final call. That's the whole craft of resizing a recipe.