Seven formulas carry almost all of culinary math. Four of them are the same division written differently, which is why they blur together in a worksheet and why the mistakes are so consistent. Here they are with the numbers filled in.
Culinary math has a reputation for being harder than it is, mostly because it is taught as a list of named formulas rather than as one habit: figure out which quantity you have and which you want, then divide in the direction that gets you there. Every formula below is that habit applied to a different pair of quantities.
1. Recipe Conversion Factor
RCF = desired yield ÷ original yield
Multiply every ingredient by the RCF. A muffin recipe yields 24 and you need 60: the RCF is 60 ÷ 24 = 2.5, so 3 cups of flour becomes 7.5 cups.
Where it goes wrong: when the portion size changes too. If the original makes 20 portions at 4 oz and you need 35 portions at 6 oz, you cannot compare 20 with 35. Convert both to total yield first — 80 oz and 210 oz — and the RCF is 210 ÷ 80 = 2.625. Comparing portion counts alone would have given 1.75 and left you a third short.
The recipe multiplier does this arithmetic on a whole ingredient list at once.
2. Yield Percentage
Yield % = (edible portion ÷ as-purchased) × 100
Five pounds of carrots, peeled and topped, come back at 4.1 pounds. 4.1 ÷ 5 = 0.82, so the yield is 82%.
Where it goes wrong: mixing this up with cooking shrinkage. Yield percentage is loss before heat — peel, seeds, stems, bone. Shrinkage is loss during cooking. They stack, in that order, and a costing that only counts one of them is wrong by the size of the other.
3. As-Purchased Quantity
APQ = edible portion needed ÷ yield %
A recipe calls for 32 oz of sliced pears and pears yield about 78%: 32 ÷ 0.78 = 41.03 oz of whole pears.
Where it goes wrong: adding the percentage instead of dividing by it. Adding 22% to 32 oz gives 39 oz, which is two ounces of pear short before you have even started, and the error grows as the yield falls. The yield percentage calculator runs it in both directions, and how much to buy for a recipe covers turning the answer into whole units at a shop.
4. Edible Portion Cost
EP cost = AP cost ÷ yield %
Broccoli at $1.80 a pound, bought as whole heads at a 61% yield, costs 1.80 ÷ 0.61 = $2.95 for every pound that reaches the plate.
Where it goes wrong: costing a recipe straight from shelf prices. Every low-yield ingredient in the dish is then under-costed, and low-yield ingredients tend to be the expensive ones — shellfish, whole fish, bone-in meat, tropical fruit. This is the formula that most often explains why a menu that looked profitable on paper is not.
5. Portion Cost
Portion cost = total recipe cost ÷ number of portions
A batch costing $48.60 that yields 18 portions works out at $2.70 a portion.
Where it goes wrong: using the yield the recipe claims rather than the yield you got. If the recipe says 18 portions and your pan produced 16, your real portion cost is $3.04. Recipes are optimistic about yield; pans are not. The cost per serving calculator and how to calculate cost per serving work through this one in detail.
6. Food Cost Percentage
Food cost % = (portion cost ÷ menu price) × 100
That $2.70 portion sold at $11.00 gives 2.70 ÷ 11.00 = 24.5%.
Where it goes wrong: dividing the wrong way round. Price divided by cost gives 4.07, which is a markup multiple, not a percentage, and it is a different number used for a different purpose. Food cost percentage is always the smaller number over the bigger one.
7. Menu Price from a Target Food Cost
Menu price = portion cost ÷ target food cost %
To hit a 30% food cost on that same $2.70 portion: 2.70 ÷ 0.30 = $9.00.
Where it goes wrong: treating the answer as the price. It is the floor. Rounding, price psychology, what the dish next to it costs and what the market will bear all move the final number, and the formula has no opinion about any of them.
All Seven Together
| Formula | Written as | Answers |
|---|---|---|
| Recipe conversion factor | desired yield ÷ original yield | What do I multiply every ingredient by? |
| Yield percentage | (EP ÷ AP) × 100 | How much of what I bought is usable? |
| As-purchased quantity | EP needed ÷ yield % | How much do I have to buy? |
| Edible portion cost | AP cost ÷ yield % | What does the usable part really cost? |
| Portion cost | recipe cost ÷ portions | What does one plate cost me? |
| Food cost percentage | (portion cost ÷ price) × 100 | How much of the price is ingredients? |
| Menu price | portion cost ÷ target food cost % | What must I charge to hit my target? |
The Pattern Worth Memorising Instead
Four of those seven are the same move: divide by a percentage to go from the smaller quantity to the larger one. Edible portion to as-purchased. As-purchased cost to edible portion cost. Portion cost to menu price. Each time you are undoing a loss or a margin, and each time the instinct to add the percentage instead produces an answer that is too small.
The other three are plain division to get a rate: a factor, a percentage, a per-portion figure. Once the two shapes are clear, the named formulas stop needing to be memorised separately, and a worksheet turns into a question about which quantity you have.
Practising Them
These work best with numbers you have to read out of a sentence rather than numbers already labelled. Our kitchen math problem generator produces fresh practice problems in five types, and there are worked sets for cost per serving, unit price, recipe scaling and measurement conversion if you would rather see solutions laid out step by step.
Frequently Asked Questions
What is the recipe conversion factor formula?
Desired yield divided by original yield. Multiply every ingredient by the result. When portion sizes differ between the two versions, convert both to total yield — portions times portion size — before dividing.
How do you calculate yield percentage?
Divide the edible portion weight by the as-purchased weight and multiply by 100. Five pounds of carrots yielding 4.1 pounds peeled is 82%.
What is the difference between AP cost and EP cost?
AP cost is what you paid per unit at the door. EP cost is what the usable portion costs, found by dividing AP cost by the yield percentage. EP cost is always the higher figure and it is the one recipe costing should use.
How do you calculate food cost percentage?
Portion cost divided by menu price, times 100. A $2.70 portion sold at $11.00 is a 24.5% food cost. Dividing the other way gives a markup multiple, not a percentage.
Do these formulas work for home cooking?
The first four do, and they are the ones that change what you put in the trolley. Portion cost is useful for meal planning; food cost percentage and menu pricing only matter if you are selling the food.