A cup of flour is not a weight
3 min read · figures checked · How we check
The same cup holds 120 g or 160 g of flour depending on how you filled it — a third more — while a cup of sugar weighs 198 g however you fill it.
One US cup of all-purpose flour weighs 120 g spooned, 148.8 g dipped and 159.6 g packed. The heaviest is a third more than the lightest, which is the difference between a loaf and a brick. Every figure here is computed by the same evaluator the calculators use, from the same sourced specification, rather than researched separately for the article. Where a number is exact by definition the article says so; where it is a measurement or a convention, it says that instead.
Why does the same cup weigh three different things?
A cup measures volume, and flour is mostly air. Spoon it in and the flour keeps the loose structure it had in the bag. Dip the cup into the bag and the walls compress what they push past, so more flour ends up inside the same space. Press it down and you get more still. Nothing about the flour changed; the packing did.
| Ingredient | Spooned | Dipped | Packed |
|---|---|---|---|
| All-purpose flour | 120 g | 148.8 g | 159.6 g |
| Bread flour | 120 g | 148.8 g | 159.6 g |
| Cocoa powder | 84 g | 104.16 g | 111.72 g |
| Granulated sugar | 198 g | 198 g | 198 g |
| Rolled oats | 89 g | 89 g | 89 g |
The last two rows are the interesting ones. Sugar and oats do not move, because their grains are hard and already sit as close together as they will go. Pressing a cup of sugar achieves nothing. Pressing a cup of flour adds a third of its weight.
Which figure does a recipe mean?
A recipe written in grams means grams and there is nothing to interpret. A recipe written in cups means whichever method its author used, and almost none of them say. The convention among American baking publishers is spooned and levelled, which is where 120 g comes from — but a home cook who dips is not doing it wrong, they are measuring a different quantity with the same word.
This is why bread recipes are the ones that fail. A cake absorbs a 20% flour error as a slightly drier crumb. A dough does not absorb it at all.
What the error does to a loaf
Take a recipe calling for four cups of bread flour and 325 g of water. Spooned, that is 480 g of flour and a dough at 67.7% hydration — a normal, slack, workable dough. Dipped, the same four cups are 595 g, and the same water now makes 54.6% hydration.
Those are not two versions of one dough. 68% is a ciabatta; 55% is a bagel. The second will not rise the way the recipe describes, will not open up in the oven, and will be blamed on the yeast. Nothing was wrong with the yeast.
| Filled by | Flour | Hydration |
|---|---|---|
| Spooning and levelling | 480 g | 67.7% |
| Dipping the cup | 595 g | 54.6% |
Not all flours weigh the same either
Even spooned and levelled, a cup is a different weight for each flour, because the particles are different sizes and shapes. Substituting one flour for another cup for cup changes the weight before it changes anything about the gluten.
| Flour | Weight |
|---|---|
| Coconut | 128 g |
| All-purpose, bread, cake | 120 g |
| Whole wheat | 113 g |
| Rye | 106 g |
| Almond | 96 g |
Swapping a cup of all-purpose for a cup of almond flour removes 24 g — a fifth of the flour — before you reach the question of whether almond flour behaves like wheat flour, which it does not.
What to do about it
Weigh it. A kitchen scale removes the entire question, which is why professional recipes are written in grams and why every serious baking book published since the mid-2000s gives both. Where you have only cups, spoon the flour into the cup and level it with the back of a knife — that is the method the 120 g figure assumes.
Where you have a recipe in cups and a scale, convert with the ingredient named rather than with a single factor. There is no such thing as "grams per cup": there is grams per cup of this thing, filled this way.
Do the arithmetic
- Grams to Cups Converter90 ingredients, spooned, dipped or packed
- Cups to grams chartThe whole table at once
- Grams to ouncesStraight weight, no ingredient involved