Walnut halves

One US cup of walnut halves weighs between 99 and 128 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 whole walnuts, walnut kernels, english walnut halves, walnuts (halves).

Two sources 29.3% apart, far outside the 10% milled tolerance, so this entry publishes the range rather than a single figure. USDA FDC 170187 (Nuts, walnuts, english, SR Legacy) publishes 1 cup halves at 99 g, implying a density of 0.4185 g/mL. King Arthur's Ingredient Weight Chart lists 'Walnuts (whole)' at 64 g per half cup, extrapolating to 128 g per cup and 0.5411 g/mL. Neither source names a specific filling method, and the physical reason for the disagreement is straightforward: whole walnut halves are rigid, irregular pieces that lock into arrangements with large air pockets. There is no equivalent to the spoon-and-sweep versus dip-and-sweep distinction that resolves flour measurement, because a half walnut cannot be sifted or spooned in the same reproducible way. Dumping halves loosely into a cup, tapping to settle, or hand-packing to fit more can shift the effective density by well over 20%. USDA's figure is consistent with a loose fill; King Arthur's is consistent with a shaken or lightly-packed fill.

The comparison with chopped walnuts is counterintuitive but instructive. This site publishes chopped walnuts at 117 g per cup, denser than the 99 g USDA figure for halves and slightly less dense than the 128 g King Arthur figure for halves. Chopping breaks the rigid geometry: small pieces fill the gaps that large halves cannot, and the resulting fill is more reproducible because the pieces self-level. This is why chopped nut weights are more consistent across sources than whole-nut weights, and why serious recipes calling for a specific weight of walnuts specify the physical form.

Walnut halves sit in the milled category despite not being milled at all. The S6 category rule assigns whole and chopped nuts to milled because they pack by scoop with air gaps, in the same way that whole seeds and grains do. The 10% category tolerance applies here, and the 29.3% gap between sources is a genuine physical disagreement rather than an arithmetic error in either source.

Related products: chopped walnuts are covered by a separate entry at 117 g per cup. Ground walnut meal, weighing approximately 80 g per cup by third-party sourcing, is not yet published here because no second independent source has been located; it will be added when the sourcing satisfies the two-source rule. Black walnuts (Juglans nigra) are a distinct species from English walnuts (Juglans regia) covered here, with different oil content, denser kernels, and no direct King Arthur reference for comparison.

No standards body publishes a bulk density for tree nuts. Codex Alimentarius standards for walnut kernels (CXS 175-1985) cover grade, moisture content and defect tolerances but not physical density. Two sources only, with a large disagreement, so this entry is held at low confidence and range-published until a third independent source can arbitrate the gap or establish that both figures reflect real but different filling methods.