Portion Calculator
Portion calculator works out Scaling factor and Scaled recipe from Portions the recipe makes, Portions you want and Ingredients, one per line. The default figures on this page give scaling factor of 2.0000; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- Scaling factor = 8 portions wanted / 4 portions in the recipe = 2.
- 2 cups flour x 2 -> 4 cups flour
- 1 tsp salt x 2 -> 2 tsp salt
- 250 g butter x 2 -> 500 g butter
- 3 eggs x 2 -> 6 eggs
Scaled recipetable
| original | amount | unit | item | scaled |
|---|---|---|---|---|
| 2 cups flour | 4 | cup | flour | 4 cups flour |
| 1 tsp salt | 2 | tsp | salt | 2 tsp salt |
| 250 g butter | 500 | g | butter | 500 g butter |
| 3 eggs | 6 | eggs | 6 eggs |
Scaled recipe, line by linetable
Its 6 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
2 sources
What the portion calculator calculates
Rescales a recipe from the number of portions it is written for to the number you want to serve, multiplying every ingredient by the same ratio and rewriting each amount in a measure you can actually use - cups into tablespoons when halving, grams into kilograms when scaling up.
How to use this portion calculator
Enter Portions the recipe makes, Portions you want, Ingredients, one per line and Rewrite awkward amounts in a better measure. Scaling factor updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Scaling factor, Scaled recipe and Scaled recipe, line by line.
The method follows Proportional scaling: each ingredient is multiplied by desired portions / original portions and NIST Handbook 44 / US legal measures, as implemented in core/units.ts.
What you can compare
Change one input at a time to see how it affects Scaling factor, Scaled recipe and Scaled recipe, line by line. The inputs you can vary are Portions the recipe makes, Portions you want, Ingredients, one per line, Rewrite awkward amounts in a better measure, A single amount to scale and Its unit.
Understanding Scaling factor, Scaled recipe and Scaled recipe, line by line
A scaling estimate. Ingredient quantities scale linearly but cooking does not: tin size, depth, baking time and oven temperature all change with batch size, and leavening, salt, spice and alcohol are often adjusted by taste rather than by ratio. Treat the scaled amounts as a starting point and use a recipe written for the larger batch where one exists.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate portion size?
Rescales a recipe from the number of portions it is written for to the number you want to serve, multiplying every ingredient by the same ratio and rewriting each amount in a measure you can actually use - cups into. Open “How this is worked out” beside the result to see each step for your own figures.
What information do I need for the portion calculator?
You need Portions the recipe makes, Portions you want, Ingredients, one per line, Rewrite awkward amounts in a better measure, A single amount to scale and Its unit. The page opens with default figures that give scaling factor of 2.0000, so you can see the scale before entering your own.
What does this portion calculator show?
It shows Scaling factor, Scaled recipe, Scaled recipe, line by line, Scaled single amount, Unit of the scaled amount, Scaled single amount, written out, Ingredient lines read and Lines with no quantity, with the working and any warnings for your entries.
Can I check how the portion calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.