Oat milk

One US cup of oat milk weighs 236.6 grams (8.3 ounces). Going the other way, 100 grams is about 0.42 cups.

One cup of oat milk weighs about 237 grams (1.000 g/mL) — essentially the density of water. All major US brands print serving-size labels of 240 mL = 240 g, converging at 1.000 g/mL. Oat milk is 88-91% water plus dispersed oat solids and, in most formulations, 2-3% added oil for body and mouthfeel. King Arthur Baking's Ingredient Weight Chart does not list oat milk, so there is no KA figure to correct here; the entry is anchored to producer-label convergence.

Oat milk is made by hydrolyzing rolled oats in water — natural enzymes convert oat starches to simpler sugars, which is why even unsweetened oat milk carries some sugar (about 7 grams per cup in Chobani Plain, 4 in Planet Oat Original, 0 in Planet Oat Unsweetened) without any added cane sugar. The slurry is then filtered and homogenized. Commercial products are typically fortified with calcium carbonate, vitamin D2, vitamin B12, and riboflavin to approximate cow-milk fortification.

USDA FoodData Central (FDC 2257046, oat milk, unsweetened, plain, refrigerated) lists this food as 91.3% water, 5.1% carbohydrate, 2.7% fat, and 0.8% protein by mass. That composition puts density essentially at water: no single component is present at high enough concentration to move density meaningfully. USDA does not publish a cup portion for this record, so the density anchor comes from producer labels. Chobani and Planet Oat both state 1 cup (240 mL) = 240 g on-label, giving density 1.000 g/mL, which reads out to 236.6 g per US customary cup (236.588 mL). The 240 mL cup on the nutrition label is the FDA labeling reference for milks and creams, not the US customary cup — the two differ by about 1.5%.

Formulation variance is real but sub-tolerance. Higher-oil formulations run slightly lighter because fat is less dense than water: Oatly Barista Edition (3% canola oil) back-computes to about 0.988 g/mL from calorie density, and Full Fat (3.7% oil) is lighter still. Lower-oil and unsweetened variants (Planet Oat Unsweetened, Oatly Low Fat) sit closer to pure water density. The Chobani Extra Creamy and Planet Oat Extra Creamy lines add more oil for mouthfeel, pushing density down marginally. All of these fall within the 5% liquid tolerance and round to 240 g / 240 mL at label precision, which is why the single-figure publish holds.

For baking substitution, oat milk swaps 1:1 by volume with cow's milk with minor caveats. Whole milk is denser at 244 g/cup (1.030 g/mL) because dissolved lactose and protein add mass; oat milk at 237 g/cup runs about 3% lighter per cup. For weight-based recipes calling for 244 g of whole milk, using 237 g of oat milk under-delivers 3% of the liquid mass — negligible for cakes, muffins, quickbreads, and pancakes, and only borderline meaningful for tight-ratio custards. Barista formulations froth better in espresso because the 3% oil emulsifies foam bubbles; Original works better in baking where the extra oil is unwanted; Unsweetened is the closest match to plain cow's milk for savory sauces and béchamel-style applications.

Shelf-stable and refrigerated versions do not measurably differ in density. Vanilla and other flavored versions add sugar (up to 9 grams per cup versus 7 for plain Original) but do not shift cup weight at label precision. Homemade oat milk blended from rolled oats and water and strained falls in the same density band, though specific weight depends on the oat-to-water ratio and strain thoroughness.