Milk

One US cup of milk weighs 244 grams. Going the other way, 100 grams is about 0.41 cups.

Also called whole milk, fresh milk, full-fat milk.

The cleanest USDA data in the dataset so far. FDC 171265 publishes a cup at 244 g, a fluid ounce at 30.5 g and a quart at 976 g, and all three give 1.0313 g/ml exactly across three different volumes. Their tablespoon at 15 g gives 1.0144 g/ml, 1.7% lower, which is the familiar whole-number rounding on a 14.8 ml spoon rather than a disagreement.

Milk is a liquid with no packing state, so one figure serves. Whole milk at 3.25% milkfat is the entry; the record with added vitamin D is used because that is what is sold in US cartons, and FDC 172217 without added vitamins publishes identical figures, so the choice does not affect the number. Skimmed and lowfat milks are slightly denser rather than lighter, because removing fat leaves proportionally more of the dissolved solids that fat displaces: USDA gives 1% milkfat at the same 1.0313 g/ml to the precision published.

King Arthur Baking's chart gives a cup of fresh milk as 8 ounces, 227 g, implying 0.9595 g/ml. That is lighter than water, and milk cannot be. It is roughly 88% water carrying lactose, protein, calcium and phosphate in solution, and dissolved solids raise a solution's density above that of the solvent; every published measurement of milk falls between about 1.03 and 1.04 g/ml.

The chart figure appears to be a cup's volume in fluid ounces read as a mass, which is why their buttermilk is also listed at exactly 227 g. The same figure would be right for water and is wrong for both. It is recorded as a rejected source under rule 7 rather than deleted, because a published figure that is wrong is worth knowing about, and this one needs no standards body to refute: the density of water is enough.

That leaves one accepted source. The entry is held at medium confidence until an independent second and third are found. Dairy composition standards regulate milkfat and solids-not-fat rather than density, so the Codex route that resolved olive oil is not directly available, though density is the basis of the lactometer readings used in dairy testing and a standards-grade figure may exist in that literature.