Flaxseed

One US cup of flaxseed weighs between 140 and 168 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 flaxseed, flax seeds, linseed, whole linseed, brown flaxseed, golden flaxseed.

Two sources 20 percent apart, far outside the 10 percent milled tolerance, so this entry publishes the range rather than a single figure. USDA FoodData Central FDC 169414 (Seeds, flaxseed, SR Legacy) publishes 1 cup whole = 168 g, implying a density of 0.7101 g/mL. King Arthur's Ingredient Weight Chart lists 'Flaxseed' at 1/4 cup = 35 g, extrapolating to 140 g per cup and 0.5918 g/mL. The USDA figure is confirmed by multiple independent mirrors of the same FDC record, each showing 168 g as the direct 1-cup-whole portion.

Whole flaxseed is small, hard and glossy — brown or golden ovals about 4 to 6 mm long — and should intuitively pack densely because small hard particles fill air gaps efficiently. Both source figures are physically possible for this seed but they imply meaningfully different fill states. The USDA figure at 0.7101 g/mL is consistent with a settled or lightly-tapped scoop where seeds have had a chance to migrate into voids. The King Arthur figure at 0.5918 g/mL is consistent with a loose scoop straight from bag to cup with no settling. Small hard seeds are unusually sensitive to this handling difference because they slide against each other easily: a firm tap or a shake can shift a cup mass by 15 to 20 percent, which is exactly the size of the observed gap. Neither source documents its method.

The contrast with flax meal published on this site is instructive. Flax meal, which is whole flaxseed ground to a coarse powder, is published here as a range of 100 to 112 g per cup, meaningfully less dense than whole flaxseed. This is the opposite of naive intuition: grinding usually seems as though it should increase density by breaking up the particles and letting them fill gaps. In practice, grinding a small hard seed into a coarse powder replaces sliding contacts between smooth ovals with static contacts between rough angular fragments, and the rough particles bridge and create voids that intact seeds do not. The same physical pattern shows up in USDA's tables for hazelnuts, where whole kernels publish at 135 g per cup and chopped kernels sit at 115 g per cup. Small whole units pack denser than their ground equivalents when the ground product is a coarse meal rather than a fine flour.

Product variants: brown flaxseed and golden flaxseed differ in seed-coat pigmentation but pack at essentially the same density and are treated as one entry here. Milled flaxseed and cold-milled flaxseed products marketed under Bob's Red Mill and similar brands are the same product category as flax meal already published on this site. Flaxseed oil, sometimes marketed as linseed oil, is a distinct product not currently covered by this site's oil entries because King Arthur does not list it and USDA data shows significant brand variation.

Flaxseed is placed in the milled category alongside other whole seeds and grains, and their milled products. The category rule tracks physical packing behavior: whole seeds pack by scoop with air gaps in the same way as whole grains and whole nuts. The 10 percent category tolerance applies here, and the 20 percent observed gap between sources is a genuine physical disagreement that likely reflects fill-method sensitivity rather than a measurement error in either source.

No standards body publishes a bulk density for flaxseed. Two authoritative sources with an over-tolerance gap and no method documentation to arbitrate, so this entry is held at low confidence and range-published until a third independent source or a documented fill method resolves the disagreement.