Why the method changes the weight
Flour is a powder full of air. Pressing on it, or scooping it out of a settled bag, squeezes some of that air out, so more flour fits in the same cup. King Arthur's measuring guide puts the range at about 120 g for a fluffed, spooned and levelled cup and up to 160 g for a densely packed one. That is a third more flour from the same cup.
USDA FoodData Central lists all-purpose flour at 125 g a cup and cake flour at 137 g for a cup that was "unsifted, dipped". Bread flour is 137 g in USDA's list and 120 g in King Arthur's. These are not errors in either source. They are different ways of filling the cup, written down.
The spoon-and-level method, step by step
- Stir or whisk the flour in its bag or canister to loosen it.
- Use a spoon to drop flour into a dry measuring cup (the kind meant to be filled to the brim) until it mounds over the top.
- Do not tap, shake or press the cup.
- Sweep a straight edge, such as the back of a knife, across the rim to level it.
NIST's kitchen tips add two points worth keeping: use a dry measuring cup for dry ingredients, not a jug meant for liquids, and strike off the excess.
When it matters
For bread and cakes, extra flour shows. A dough with a third more flour than intended is stiffer and drier; a cake with too much flour bakes up dense. For thickening a sauce or dusting a counter, it hardly matters.
The question to ask is how the recipe's author measured. A recipe that gives grams has answered it. A recipe from a source that publishes a weight chart, such as King Arthur, can be matched by using that chart. A recipe with cups and no hint is a guess; spoon-and-level is the usual US assumption, and 120 g a cup is the matching weight.
Weighing is simpler
A scale removes every one of these variables. NIST's metric kitchen recommends measuring by mass for exactly this reason. To move your own recipes to weights:
- Convert each flour line once with the grams to cups converter, using the flour type you bake with.
- Bake the recipe once by weight and note the result.
- Write the grams next to the cups so you never convert it again.
The guide to converting a recipe to grams goes through a whole recipe line by line.
Flour weights per cup
| Flour | Grams per US cup (used) | Published figures |
|---|---|---|
| All-purpose flour | 120 | KA 1 cup = 120 g USDA 1 cup = 125 g |
| Bread flour | 120 | KA 1 cup = 120 g USDA 1 cup = 137 g |
| Cake flour | 120 | KA 1 cup = 120 g USDA 1 cup = 137 g |
| Whole wheat flour | 113 | KA 1 cup = 113 g USDA 1 cup = 120 g |
| Self-rising flour | 113 | KA 1 cup = 113 g USDA 1 cup = 125 g |
| Almond flour | 96 | KA 1 cup = 96 g |
| White rice flour | 142 | KA 1 cup = 142 g USDA 1 cup = 158 g |
The flour rows of the full table on the grams to cups page give every flour in the converter, with both sources.