Rolled oats

One US cup of rolled oats weighs between 81 and 89 grams, 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 old-fashioned oats, quick-cooking oats, porridge oats.

Two sources 9.4% apart, over the 5% tolerance for the grain category, so this entry publishes a range rather than a figure. USDA FDC 173904 gives a cup of dry regular and quick oats at 81 g (0.3424 g/ml). King Arthur's Ingredient Weight Chart gives old-fashioned or quick-cooking oats at 89 g per cup (0.3762 g/ml).

Neither source names a method, and no third source was found that measures the same product independently. Foundation Foods entry FDC 2346396 (Oats, whole grain, rolled, old fashioned, published October 2022) is the newer, more rigorous USDA record but publishes only per-100 g data and no cup portion, so it cannot supply a cup weight under rule 3. The wider issue is that rolled oats covers a range of physical products with meaningfully different densities.

King Arthur's own house-brand rolled oats appear on the same chart at 113 g per cup, 24% heavier than their generic figure, because that flake is thicker and denser than the standard supermarket old-fashioned oat. Retail labelling matches USDA more closely than King Arthur's generic figure: Quaker Oats declares its old-fashioned serving as 40 g per half-cup dry (80 g per cup), and Bob's Red Mill's organic old-fashioned rolled oats declare 40 g per half-cup as well. Nutrition-label servings are rounded and cannot serve as sources under rule 3, but the consistent rounding to the same figure across major brands is evidence that USDA's 81 g reflects the typical retail product and King Arthur's 89 g reflects a denser specification.

Rolled oats are placed in the grain category matching white rice, not the milled category with flour and cocoa. They are flattened whole oat groats, not a ground powder, and their bulk density is affected by how they settle in the cup in the same way rice kernels are, but more so because the flakes have larger surface area and both bridge and compress. The 9.4% spread observed here is consistent with that behaviour and does not warrant a wider tolerance category invented for this entry alone.

Steel-cut oats are a separate product covered by a separate entry. USDA lists FDC 2346397 (Oats, whole grain, steel cut, Foundation Foods) and King Arthur gives 70 g per half-cup (140 g per cup), roughly 65% higher density than rolled oats because the grain is chopped rather than flattened and retains its whole-grain density. Cooked oats are also a separate product; USDA FDC 173905 gives cooked oats at 234 g per cup, roughly three times the dry weight, because the grain absorbs water during cooking.

No standards body publishes a bulk density for rolled oats. Grain trading uses test weight in pounds per bushel for whole groats, but this is measured on a different apparatus for a different physical form (whole intact oats before rolling) and cannot serve as a source under rule 3. Two sources only, and the range is published because no third source arbitrates the disagreement.