All-Purpose Flour: US cups to grams

All-purpose flour is the most miscalculated ingredient in home baking, and the reason is mechanical, not chemical. Flour is a low-density powder that compresses under its own weight. The exact same cup of flour can weigh anywhere between 113 and 150 grams depending on a single decision the baker made before they ever picked up the measuring cup, which is how they got the flour into it.

When you scoop a measuring cup directly into the flour bag and shake the cup against the side to level it, you compress the flour. King Arthur's test kitchen measures this scoop-and-shake method at roughly 150 grams per US cup. When you spoon the flour gently into the cup and slide a knife across the rim to level, you get 125 grams. When you sift the flour into the cup and level without tapping, you get 113 grams. That is a thirty-three percent spread for the same nominal one cup, and it is the reason a recipe written for sifted flour produces a dense brick when prepared with scooped flour and a soup when prepared the other way around.

The single most common conversion mistake is treating "1 cup" as a fixed weight. It is not. It is a volume, and a volume of an irregular powder is a function of how the powder is loaded into the container. Recipe authors are inconsistent about which method they assume, which means a converted recipe is only as accurate as the base assumption. King Arthur, USDA, and Cook's Illustrated all settled on 125 grams as the spooned and leveled standard, and that is the figure this site defaults to.

The correct technique for spooned and leveled measurement is to give the bag a brief stir with a fork or whisk to break up any settled compression, then spoon the flour into the cup without tapping or shaking, mounding it slightly above the rim. Drag the back of a knife or a flat scraper across the rim in a single pass, letting the excess fall back into the bag. Do not tap the cup on the counter to settle the flour. Tapping is what turns 125 grams into 145.

Density matters most in baking applications where the ratio of flour to liquid determines the final structure. Yeast breads and pancakes are reasonably forgiving because the dough or batter can absorb extra flour and still rise. Cookies, biscuits, and especially cakes are unforgiving. A cake recipe calling for 2 cups of flour will fail noticeably if you give it 250 grams instead of 300, and it will fail differently if you give it 250 grams of bread flour instead of all-purpose because the protein content shifts the gluten development and the crumb tightens.

This site separates the two questions. The ingredient is all-purpose flour. The variant is the loading method. If your recipe specifies "1 cup, spooned and leveled" you want the 125 gram figure. If the recipe was written by King Arthur after 2022, they may be using their newer 120 gram standard, in which case the headline figure is 5 grams light. Five grams is real but rarely consequential. If the recipe specifies "1 cup, sifted" you want 113. If the recipe was written by a grandparent and just says "1 cup" without context, the safe assumption is spooned and leveled at 125, and the safer move is to weigh the flour from the start and stop guessing.

All-purpose flour from different mills also differs slightly. Bob's Red Mill publishes 130 grams per cup. King Arthur publishes 120 grams per cup as of their most recent revision. The difference comes from the exact wheat blend, moisture content, and how finely the flour is milled. For the converter, 125 grams remains the canonical default because it sits between the two and matches the published USDA figure.