What this calculator works out
Give it what the recipe serves and what you need it to serve, and it works out the factor to multiply your ingredients by.
The arithmetic is trivial. The useful part is knowing where to stop applying it. Flour, butter, liquid and meat all scale straight. Salt, chilli, cooking time and tin size do not, and those are where a doubled recipe usually goes wrong.
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Before you scale
- Most ingredients scale straight. Flour, sugar, butter, liquid, meat and vegetables all multiply by the same factor.
- Several things do not. Seasoning, raising agents, alcohol, strong spices, cooking time and tin size all need judgement.
- Weigh rather than measure by volume when scaling. Errors multiply along with everything else.
A doubled cake in a doubled tin is deeper, not wider, so it needs a lower temperature and a longer time. Salt and chilli scale faster than the palate expects, so start at around three quarters and adjust. Raising agents scale straight but their effect does not, because a deeper mixture resists rising. And a pan that is too crowded steams rather than browns, which changes the dish rather than just its size.
How this calculator works
Factor = target servings ÷ original servings
New quantity = original quantity × factorThe arithmetic is one division and one multiplication. The value is in applying the same factor consistently and in knowing where to stop applying it.
The calculator also flags the cases where the factor should not simply be carried across: seasoning above about 1.5×, cooking vessels, and timing.
Worked example: four to six
- Factor: 6 ÷ 4 = 1.5
- 250 g flour becomes 375 g
- 2 eggs becomes 3 — convenient here, but scaling eggs often lands on a fraction
- 1 teaspoon of salt becomes 1.5 teaspoons on paper. Start with about 1¼ and taste.
- A 20 cm tin holds 1.5 times less than the mixture now needs. Use a 24 cm tin, or accept a deeper cake and a longer, cooler bake.
Handling eggs and awkward quantities
Eggs are the usual sticking point, because they come in whole units. A factor of 1.5 applied to 3 eggs gives 4.5.
- Beat one egg, weigh it, and use the fraction you need. A medium egg out of its shell is roughly 50 g.
- Or round to the nearest whole egg and adjust the liquid slightly to compensate.
- For cakes, rounding up gives a slightly richer, softer result; rounding down a slightly drier one.
The same approach works for anything sold in units — tins, packets, sausages. Round to what you can buy and adjust the flexible ingredients around it.
Common mistakes
- Scaling the seasoning by the full factor. Salt, chilli and strong spices are the commonest way a scaled-up dish goes wrong.
- Scaling the cooking time. A double quantity does not take double the time. It usually takes somewhere between the same and half as long again.
- Keeping the same tin. Depth changes how heat reaches the centre.
- Overcrowding the pan. Twice the meat in the same pan steams instead of browning. Use two pans or cook in batches.
- Scaling by volume instead of weight. Small measuring errors multiply with everything else.
- Scaling a recipe down too far. Below about half, thin layers and small quantities behave differently and some recipes stop working entirely.
Frequently asked questions
Can I just double everything?
For most ingredients, yes. Not for salt and strong spices, which should start at around three quarters of the scaled amount and be adjusted by taste. Not for cooking time, which rises far less than proportionally. And not for the tin or pan, which needs to grow in area rather than just take a deeper filling.
How do I scale cooking time?
Not by the same factor. A dish twice the size in the same shaped vessel usually needs somewhere between the same time and half as much again. If the depth increases, drop the oven temperature by 10 to 20°C and extend the time, so the centre cooks before the outside dries.
What do I do about half an egg?
Beat a whole egg, weigh it, and use half the weight. A medium egg out of its shell is roughly 50 g, so 25 g is about half. If precision is not critical, round to a whole egg and adjust the other liquid a little.
Does baking scale as well as cooking?
Less well. Baking depends on ratios and on how heat reaches the centre of a fixed mass, so changing the quantity changes the geometry. Scaling by up to double is usually fine with a tin adjustment. Beyond that, it is often more reliable to bake two batches than one large one.
Can I scale a recipe down?
Down to about half, usually without trouble. Below that, thin layers cook faster and dry out, small amounts of liquid evaporate proportionally more, and some methods stop working at all. Reduce the cooking time and check early.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
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References
These organisations publish the guidance and figures behind this page.
- Food Standards Agency — UK food safety guidance for home cooks and businesses
- NHS — eat well — portion guidance and healthy eating advice
Sources are checked at publication and can change — how I choose and check references.