Mustard seeds

One US cup of mustard seeds weighs between 159 and 200 grams (5.6 to 7.1 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.

Spice seeds compared: cup weights side by side, the source behind each, and why they differ.

TL;DR: Whole yellow mustard seeds span 159-200 grams per cup across producer labels and USDA branded records, driven by seed variety, size, and pack density. The Chef's Resources 181 g/cup sits mid-range and is a reasonable working figure, but the honest 26% spread means no single number covers the shelf. Whole mustard seeds pack roughly 60-100% denser than ground mustard (101 g/cup in the paired entry) because solid spherical seeds nest tightly while ground powder bridges and traps air — the same solid-seed pattern documented for cumin.

Mustard seeds come from three species: yellow or white mustard (Sinapis alba, the mildest, most common in Western pickling and American cuisine), brown mustard (Brassica juncea, hotter, standard in Indian and Chinese cooking as sarson or rai), and black mustard (Brassica nigra, hottest, historically dominant but now less common due to harvest difficulty). Retail bags labeled simply "mustard seeds" are usually yellow. The seeds are small dense spheres roughly 1-2 mm in diameter for yellow varieties, slightly smaller for brown and black. Whole seeds are used in pickling brines, tempering (tarka) for Indian dishes, seafood boils, sausage seasoning, and coarse-grain mustard preparations. Their flavor and heat only develop after crushing or exposure to water, so whole seeds themselves are mild.

The density spread across sources reflects real physical variance. Gneiss Spice and Savory Spice retail labels give the low end at 159-162 g/cup. Chef's Resources' oz-per-cup table gives 181 g/cup — a mid-range direct measurement. USDA Global Branded Food Products Database UPC 725677220161 measures a Frontier-adjacent brand at 192 g/cup. Marnamaria Spices sits at the high end (200 g/cup) with a pouch-fill measurement that may reflect tapped-cup convention rather than spooned-and-leveled. USDA SR Legacy is silent on whole mustard seed, publishing only the ground form (107 g/metric cup, matched to the paired ground-mustard entry at 101 g/cup) — the same USDA pattern seen for coriander and cumin, where ground has cup portions but whole does not.

Physical reasoning supports both the observed range and the dramatic whole-vs-ground contrast. Yellow mustard seeds contain roughly 26% protein, 28-36% fat (mostly as fixed oil), 15-20% carbohydrate, and 6-9% moisture. Their true particle density is around 1.05-1.1 g/mL — dense oil-seed material. Bulk cup density lands at 60-80% of particle density (159-200 g/cup = 0.67-0.85 g/mL), consistent with efficient packing of small dense spheres. Small round seeds nest into inter-seed voids far better than irregular flakes or granules do, so the whole-seed cup density is genuinely high.

Ground mustard, by contrast, publishes at 101 g/cup — roughly half the whole-seed density. Grinding takes dense, tightly-packing spheres and reduces them to fine cohesive powder that bridges and traps air pockets. This is the opposite direction from coriander, where whole seeds have internal schizocarp cavities that collapse when ground, producing denser ground powder than whole. Coriander (hollow seed) becomes denser when ground; mustard, cumin, and other solid seeds become lighter. This morphology-based rule is a useful physical prediction for future whole-vs-ground seed comparisons.

King Arthur Baking is silent on mustard seeds in any form. The chart focuses on baking staples, and whole mustard seeds are a pickling and savory-cooking ingredient rather than a bread or cake component. No KA correction opportunity exists here, but the absence is worth noting for cooks who assume KA's chart covers all common seasonings.

For practical use, 180 g/cup (roughly the Chef's Resources midpoint) is a reasonable working figure for recipe scaling of yellow mustard seeds. A tablespoon runs about 11 grams, a teaspoon about 3.7 grams. Brown mustard seeds pack slightly denser than yellow due to smaller size and marginally higher oil content; black seeds slightly denser still. When exact measurements matter — for a pickling brine that needs precise brine-to-solids ratio, or for a large-batch Indian tempering — weigh by grams rather than measuring by volume. For casual home cooking (a pinch in a vinaigrette, a spoonful in a curry), cup measurements work fine within the noise floor of the dish.