Soy Flour

One US cup of soy flour weighs between 84 and 140 grams (3 to 4.9 ounces), depending on how the cup is filled and which source measured it. That range is the answer; a single number would not be. Every figure behind it is below, with the method each source used.

Also called soya flour, full-fat soy flour, whole grain soy flour, soybean flour, kinako.

Soy flour weighs anywhere from 84 to 140 g per US cup (3 to 4.9 oz) depending on whose figure you take. USDA measures stirred full-fat soy flour at 84 g, the Bob's Red Mill and Hodgson Mill bags print 28-30 g per quarter cup (112-120 g), and King Arthur lists 140 g. The sources disagree by far more than the 10% tolerance, so this entry publishes the range.

Soy flour is ground from soybeans. The flour sold for home baking, Bob's Red Mill and Hodgson Mill's organic whole grain, is full-fat: USDA puts it at 38% protein, 21% fat and 32% carbohydrate, with only 5% water. Defatted soy flour, the industrial ingredient left after the oil is pressed out, is a different product at 51% protein and 1% fat. Bakers use soy flour to add protein and moisture to bread and gluten-free mixes and as an egg replacer; roasted soy flour is sold as kinako for Japanese sweets.

USDA SR Legacy records full-fat raw soy flour (FDC 174273) at 84 g per cup stirred and 5.2 g per tablespoon, and full-fat roasted (FDC 174274) at 85 g stirred. Defatted soy flour (FDC 174275) weighs more, 105 g per cup, because without the oil the particles are denser and pack tighter. "Stirred" means the flour is loosened before it is spooned into the cup, which is how a careful baker measures.

The labels sit much higher. Bob's Red Mill prints a quarter cup at 28 g, one ounce, and Hodgson Mill at 30 g. The US reference serving for flours is a weight, and labels tend to print that weight next to the nearest household measure, so a label quarter cup is not a measured quarter cup. King Arthur's 35 g per quarter cup, 140 g per cup, is the heaviest figure of all and says neither full-fat nor defatted.

Physically, full-fat soy flour is an unusual powder. It is fine and slightly oily, so it clumps, and its 21% fat makes the particles lighter than wheat flour's. USDA's stirred cup, 0.355 g/mL, is much lighter than a cup of all-purpose flour at about 0.5 g/mL, while King Arthur's 0.59 g/mL would make it heavier than any wheat flour on this site. Packing the cup, scooping straight from the bag or letting the flour settle in storage can each add a third to the weight, so the range here is mostly a range of methods.

Practical guidance: weigh soy flour. Recipes that give it in grams have usually been tested; recipes that give cups rarely say how they filled them. If you only have cups, spoon the flour in loosely and level it for about 85-90 g, the USDA end of the range; a scooped cup will land nearer the labels' 112-120 g. When replacing part of the wheat flour in bread, swap by weight, typically no more than 10-15% of the flour, because soy has no gluten.