Every conversion table answers to one hidden question: how full is a cup? For water, physics decides. For flour, technique does — and the spread between techniques is the single largest error in home baking.
The flour experiment
Scoop the measuring cup straight into the flour bag (packing as you go): 140–150 g. Spoon flour into the cup and level with a knife: 120–125 g. Sift first: 110 g. The same "one cup" spans 25% — and flour recipes are calibrated to the middle number. A scooped-cup cookie dough is a drier dough than the author tested; the cake is denser; the bread is thristier than planned.
Why volume persists
- Liquids forgive it: water, milk, and oil measure fine by volume — the habit forms where it works.
- American recipes are volume-native: written for cups, tested in cups — until the author converts to weights after enough mail.
- Scales felt fancy; now a $10 digital scale is cheaper than the failure it prevents.
The standard, stated
| Technique | AP flour per cup | Error vs recipes |
|---|---|---|
| Scooped (dip and pack) | 140–150 g | +20% |
| Spooned and leveled | 120–125 g | the standard |
| Sifted then measured | 110 g | −10% |
Every weight in this database assumes spooned-and-leveled — the convention professional recipes mean by "1 cup."
The transition, one recipe at a time
- Buy the scale ($10–20, 1 g resolution).
- Zero (tare) the bowl — the button that makes all of this easy.
- Convert your most-baked recipe with this database, once, and write the weights in the margin.
- Notice the repeatable results and never look back.
Weighing is not precision for its own sake — it is the difference between following a recipe and re-rolling dice with flour every time you bake.