The short answer: one US cup of all-purpose flour weighs about 120 grams, measured the standard way (spooned into the cup and leveled). But the full answer is more interesting, because "about" is doing real work in that sentence — and because different flours weigh different amounts.
Conversion chart by flour type
| Flour type | 1 cup | ½ cup | ¼ cup |
|---|---|---|---|
| All-purpose flour | 120 g | 60 g | 30 g |
| Bread flour | 127 g | 64 g | 32 g |
| Cake flour | 114 g | 57 g | 29 g |
| Whole wheat flour | 128 g | 64 g | 32 g |
| Rye flour | 102 g | 51 g | 26 g |
| Almond flour | 96 g | 48 g | 24 g |
Why your cup of flour might weigh 150 grams
Flour compresses. If you scoop the measuring cup directly into the flour bag — the way most of us learned — you pack the flour down and can easily end up with 140–150 g in a "120 g" cup. That's 20% extra flour, and it's the single most common reason home-baked cakes turn out dense and cookies turn out dry. The recipe wasn't wrong; the cup was.
To measure flour by volume correctly: fluff the flour in its container first, spoon it into the measuring cup without packing, and level the top with the back of a knife. Done this way, your cup will land close to the standard 120 g.
The better fix: weigh it
Professional bakers don't argue about scooping technique — they use a scale. A digital kitchen scale removes the ambiguity entirely: 120 g is 120 g no matter how it got in the bowl, recipes become perfectly repeatable, and you dirty fewer measuring cups. If you bake even a few times a month, it's the cheapest meaningful upgrade you can make.
A note on cups themselves
This chart uses the US legal cup (240 ml). Australian recipes use a 250 ml cup and Japanese recipes a 200 ml cup, so a "cup" in a recipe from abroad may not be the cup in your drawer — one more argument for grams. If a recipe gives weights, always prefer them.
Need to convert sugar, butter, honey or cocoa too? The baking unit converter knows the density of each. And if you're resizing the whole recipe, the recipe scaler will recalculate every ingredient at once.