Fennel Seeds

One US cup of fennel seeds weighs between 92.7 and 104.6 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 fennel seeds, whole fennel seeds, saunf, sonf, moti saunf, fennel seed.

TL;DR: Whole fennel seeds land in the 93-105 grams per cup range across USDA and producer measurements, driven by the settling-method sensitivity of elongated crescent-shaped seeds. The USDA SR Legacy anchor sits at 93 g/cup, USDA branded records at 96 g/cup, and Chef's Resources at 105 g/cup — a 13% spread that matches the pattern seen for cumin seeds and other elongated spices where whole-seed density depends on how the cup was filled.

Fennel seeds come from Foeniculum vulgare, a Mediterranean-native herb in the parsley family cultivated worldwide for its sweet licorice-flavored seed. The seeds are actually dry schizocarp fruits: elongated green-yellow crescents 5-10 mm long with prominent longitudinal ridges. Turkish and Egyptian fennel produces slightly plumper seeds with higher anethole content (the compound responsible for the licorice flavor); Indian fennel (saunf) has smaller seeds with a milder profile and is often eaten as a post-meal digestive. The seeds are essential in Italian sausage, Indian tempering (tarka), Chinese five-spice, French bouillabaisse, and countless Mediterranean fish and pork preparations.

The density spread reflects genuine physical variance. USDA SR Legacy's laboratory measurement of whole fennel seed (FDC 171323) gives 98 g/metric cup, which converts to 93 g/US cup — a firm anchor for the low end. USDA Global Branded Food Products Database entry UPC 026662550981 measures a branded product at 96 g/US cup, essentially confirming the USDA SR figure within measurement noise. Chef's Resources' oz-per-cup table lists fennel seed at 3.69 oz/cup (105 g/cup), roughly 13% above the USDA anchor. This spread is consistent with the well-documented settling-method sensitivity of elongated seeds: loose-fill measurements land near 93-96 g/cup, while tapped or heaping-fill measurements approach 105 g/cup.

Physical reasoning explains both the density range and its variance. Fennel seeds contain roughly 15% protein, 15% fat (dominated by the volatile anethole-rich essential oil), 40-52% carbohydrate (mostly fiber), and 6-9% moisture. True particle density is around 0.9-1.1 g/mL. Bulk cup density lands at 40% of particle density (93-105 g/cup = 0.39-0.44 g/mL) because the elongated crescent shape prevents efficient inter-particle packing. Fennel seeds settle with more void space than round seeds like mustard (159-200 g/cup, ~1.7x denser per cup despite similar per-seed mass) because crescents bridge each other and leave gaps that spherical seeds would fill. Tapping or shaking the cup partially collapses this void structure, adding 10-15% to the measured density — hence the CR high-end figure.

Two USDA GBFD records are rejected as outliers. Morton & Bassett fennel seed (UPC 016291441231) at 134 g/cup sits 44% above the USDA anchor and outside plausible bulk density for elongated seeds — likely a tapped-fill or FDA serving-size rounding artifact. A separate branded record (UPC 718343230557) at 192 g/cup is physically impossible: no whole fennel seed packs at twice particle density, and this figure would require negative void fraction. Almost certainly a data-entry error, possibly confusing fluid-ounce vs mass-ounce or mislabeling a ground-fennel figure as whole seed. Neither is treated as legitimate alternative data.

King Arthur Baking is silent on fennel seeds. The chart focuses on baking staples, and fennel seed is a savory Italian, Indian, and Mediterranean cooking spice rather than a bread or cake component. No KA correction opportunity exists here.

The fennel-seed range sits alongside the paired ground-fennel category (Chef's Resources gives 106 g/cup for the ground form, so ground fennel is nearly identical in cup density to whole fennel). This is unusual for solid seeds — cumin and mustard both become significantly lighter when ground, because their whole-seed forms pack tightly and ground powder bridges more air. Fennel is different because whole fennel seeds already pack loosely due to their crescent shape, so grinding does not create a large density change. The tight whole/ground similarity is a useful physical prediction for future elongated-seed spice additions.

For practical use, 96-100 g/cup is a reasonable working figure for recipe scaling of whole fennel seeds. A tablespoon runs about 6 grams, a teaspoon about 2 grams. Turkish and Egyptian fennel packs slightly denser due to plumper seeds; Indian saunf packs slightly lighter due to smaller seeds. When precision matters — for a large batch of Italian sausage where seed-to-meat ratio drives flavor, or for a spice blend where fennel is a primary note — weigh by grams. For casual home cooking (a pinch in a curry base, a spoonful crushed into vinaigrette), cup measurements work fine within the noise floor of the dish.

The following published figures for fennel seeds are rejected here, with the physics or standards reasoning behind each rejection on its own page:

• USDA Branded (Fennel Seed, Morton & Bassett): 134 g per cup
• USDA Branded (Fennel Seeds, unspecified brand): 192 g per cup