Peanut butter

One US cup of peanut butter weighs 258 grams. Going the other way, 100 grams is about 0.39 cups.

Also called smooth peanut butter, creamy peanut butter, natural peanut butter.

Sources agree within 4.5%, inside the 5% fat category tolerance but close to it. USDA FDC 172470 gives a cup of smooth peanut butter without salt at 258 g (1.0905 g/ml) and a tablespoon at 16 g (1.0821 g/ml, back-calculated from the 32 g per 2 tbsp portion), a spread of 0.77% that indicates the two USDA figures are one density rounded twice rather than two measurements. King Arthur's Ingredient Weight Chart gives 135 g per half cup, implying 270 g per cup or 1.1412 g/ml.

Peanut butter is placed in the fat category alongside butter and the oils because its measurement behaviour is fat-like rather than powder-like: it is a plastic solid at room temperature that deforms under pressure and does not compact meaningfully during filling. It is not chemically fat, being roughly 50% oil by weight with the balance in peanut solids, but the category assignment is about how the substance interacts with a measuring cup rather than its composition. Peanut butter differs from butter in one important way: US butter is sold in cup-marked wrappers, so the cup weight reflects the packaging convention and is exceptionally consistent across sources.

Peanut butter jars carry no such markings, so cup weight is a real measurement of how the substance fills a vessel, and the residual measurement variation is what accounts for the USDA-King Arthur disagreement. Retail nutrition labels for the major smooth peanut butter brands (Jif, Skippy, and generic equivalents) declare 32 g per 2 tablespoons, matching the USDA portion to the nearest gram. Label figures do not qualify as sources under rule 3 because they round on a small measure, but the fact that the consumer standard matches USDA rather than King Arthur is evidence that USDA reflects typical fill and King Arthur measured a more forcefully packed cup.

Natural peanut butter (containing only ground peanuts and salt, with no added palm oil or emulsifier) separates on standing and must be stirred to reintegrate the oil before measuring; the density above assumes a stirred and homogeneous jar. Chunky and crunchy peanut butter are separate products and are not covered by this entry: USDA FDC 172473 lists chunk style at 258 g per cup, the same figure as smooth, but the presence of peanut chunks makes cup filling less repeatable and warrants a separate entry with its own sourcing. Reduced-fat peanut butter typically contains added maltodextrin and other bulking agents that increase density, and is also outside the scope of this entry.

No standards body publishes a bulk density for peanut butter. FDA identity standards (21 CFR 164.150) specify that peanut butter must contain at least 90% peanuts and cover permitted additives, but not physical density. Two sources only, so this entry does not meet rule 2 and is held at medium confidence until an independent third is found.