A US cup is 236.6 ml of volume, so its weight depends entirely on what is in it. One cup of plain flour is about 125 g, white sugar 200 g, butter 227 g and honey 340 g. There is no single conversion factor, which is why a cups-to-grams chart has one row per ingredient rather than one number.
Worse, the flour figure assumes a particular way of filling the cup, and recipes almost never say which.
Why does a cup of flour vary so much?
Because flour compacts. The 125 g convention behind most American recipe development is spoon-and-level: spoon flour loosely into the cup and scrape the top flat with a knife. Dipping the cup into the bag and levelling it packs the flour and can give 150 g or more from the same cup.
That is a 20 per cent difference in the main structural ingredient of a cake, arriving from nothing but technique. It is the single largest source of variation in baking from American recipes, and it is invisible to anyone following the instructions exactly as written.
| One US cup of | Approximate weight |
|---|---|
| Plain flour, spooned | 125 g |
| Granulated sugar | 200 g |
| Brown sugar, packed | 220 g |
| Butter | 227 g |
| Honey | 340 g |
| Water | 237 g |
Which tablespoon is it?
Fifteen millilitres almost everywhere, and twenty in Australia. Three teaspoons make a tablespoon and sixteen tablespoons make a US cup, so the internal arithmetic is consistent — until the tablespoon itself changes size.
The Australian tablespoon is the trap. At 20 ml it is a third larger than everyone else’s, so an Australian recipe asking for two tablespoons of a strong ingredient — baking soda, salt, vanilla — is asking for noticeably more than a British or American cook would give it.
The metric cup is the other mismatch: 250 ml in Australia and parts of Europe against 236.6 ml in the United States. Close enough to substitute in a stew and not in a cake.
How do you scale a recipe?
Multiply everything by the target servings divided by the original. Going from 4 to 6 is a factor of 1.5, so 250 g becomes 375 g — and then the method needs judgement rather than arithmetic.
Three things do not scale linearly.
- Pan size. Doubling a cake and using the same tin gives a batter twice as deep, which burns at the edge before the middle sets. Two tins is almost always the answer.
- Cooking time. A larger volume takes longer and not proportionally. Check early and use a probe or a skewer rather than the clock.
- Salt and strong flavours. These often want slightly less than the factor suggests, particularly when scaling up substantially.
Halving has its own arithmetic, which the recipe-halving article covers — the short version being to move down a unit rather than looking for a fraction that does not exist on a measuring cup.
What about calories per serving?
Total recipe calories divided by servings. A 2,400 kcal dish serving six is 400 per portion, and if the cooked dish weighs 1,800 g that is 133 kcal per 100 g.
The per-100-gram figure is the one worth keeping, because it survives a disagreement about serving size. "One serving" is a decision rather than a measurement — a dish that serves six generously serves four honestly — and weighing the cooked total once gives a figure that works for any portion afterwards.
It also handles the case where the dish is eaten over several days at different portion sizes, which is the normal case rather than the exception.
Should you just weigh everything?
For anything dry, yes, and it removes this entire class of problem. A digital scale costs very little, weighing is faster than washing three cup measures, and it makes a recipe reproducible in a way volume never does.
Liquids are the exception where volume holds up well: a millilitre is a millilitre regardless of technique, and for water one millilitre is one gram anyway. The rule of thumb is to weigh solids and measure liquids, and to weigh liquids too when the recipe is a ratio rather than a list.
Questions people ask
Is a US cup the same as a metric cup? No — 236.6 ml against 250 ml, a difference of about 5.7 per cent. It matters in baking and rarely elsewhere.
Why do British recipes use grams? Because British recipe writing standardised on weight for dry ingredients, which is more reproducible. It is why a British recipe converted to cups is usually less reliable than the original.
Does sifting change the weight? Not the weight, only the volume. A cup of sifted flour weighs less than a cup of unsifted flour, which is exactly the problem weighing removes.
How do I scale a recipe by a third? Multiply by 0.667 and round sensibly. Where an ingredient is an egg or another whole unit, scale by two thirds or one and a half instead so the whole numbers work out.
Weigh the dry, measure the wet, and check which tablespoon a recipe means. The cups to grams converter carries a weight per ingredient, the cooking conversion chart covers spoons and cups across the three systems, the ingredient scale calculator applies a factor to a whole recipe, and the calories per serving calculator gives both the per-portion and the per-100-gram figure.