These questions ask you to enlarge or reduce a recipe without changing its proportions. Sometimes the target number of servings is given; sometimes a new amount of one ingredient tells you how large the batch has become.
Find the batch factor first
Treat the original recipe as the base. When the yield changes, calculate target servings divided by original servings. When an ingredient amount changes first, calculate new amount divided by original amount. That quotient is the batch factor. Multiply, rather than add, whenever you transfer the factor to another ingredient. Units stay attached to ingredient amounts and do not enter the serving ratio.
| Given information | Method | Tiny example |
|---|---|---|
| Original and target servings | Factor equals target servings divided by original servings; multiply each original ingredient amount by it. | A five-serving recipe uses 180 grams of an ingredient. Eight servings use a factor of 1.6, so the new amount is 288 grams. |
| Original and new amount of one ingredient | Factor equals new amount divided by original amount; multiply the original yield and every other ingredient by it. | An ingredient rises from 300 to 425 millilitres, a factor of 17 divided by 12. A twelve-serving base therefore becomes 17 servings. |
| A stated number of batches | Use the stated batch multiplier directly on every ingredient. | Making 1.75 batches from 240 grams requires 240 times 1.75, which is 420 grams. |
After scaling, check one ratio. New ingredient amount divided by original ingredient amount should equal new servings divided by original servings. For several ingredients, every ingredient must give that same factor. A factor below one is normal for a reduced recipe, and a non-integer factor is just as valid as a whole-number multiplier.
Reject the tempting wrong routes
| Tempting route | How to reject it |
|---|---|
| Add the number of extra servings to an ingredient amount. | Servings and grams or millilitres are different units. Convert the serving change into a multiplier before changing an ingredient. |
| Add the target serving count itself to an ingredient amount. | The target count is not an ingredient increase. Divide it by the original count to find the multiplier instead. |
| Scale one ingredient correctly but give another a different factor. | Divide each proposed new amount by its original amount. A preserved recipe gives the same quotient every time. |
| Estimate a familiar fraction of the original batch instead of calculating it. | Find the exact ratio of the new amount to the old amount, then apply it to the servings. Check by multiplying back. |
Try it
A soup recipe for 6 servings uses 450 millilitres of milk. How many millilitres are needed for 14 servings at the same recipe proportions? Enter the number of millilitres.
A stew recipe uses 630 millilitres of stock for 9 servings. If 980 millilitres of stock is used and all other ingredients are scaled to match, how many servings does the batch make? Enter the number of servings.
A pasta recipe for 3 servings uses 90 grams of cheese and 150 grams of pasta. A larger batch uses 330 grams of cheese with both ingredients scaled equally. How many grams of pasta does it use? Enter the number of grams.