Vegetable oil

One US cup of vegetable oil weighs 218 grams. Going the other way, 100 grams is about 0.46 cups.

The bottle labelled 'vegetable oil' on a US supermarket shelf is not one thing. Most brands are refined soybean oil; some are canola; some are soy-canola blends; a small number are corn or sunflower. The one thing they have in common is that they are all liquid at room temperature and all sit at essentially the same density — between 0.917 and 0.923 grams per millilitre, a range narrow enough that the specific oil almost never matters for measurement.

USDA FoodData Central publishes 1 cup of soybean oil at 218 grams and 1 tablespoon at 13.6 grams (FDC 173573, Oil, soybean, salad or cooking). Canola oil (FDC 173571) publishes the same 218 grams per cup within a fraction of a percent. Density comes out to 0.9214 grams per millilitre either way. This matches the physical density of pure triglyceride oils at 20 degrees Celsius, which the Codex Alimentarius standard for named vegetable oils (CXS 210-1999) publishes for each type as part of the identity specification. Standards agree because the underlying molecules — long-chain fatty acid triglycerides — have similar molecular volumes regardless of which plant they came from.

King Arthur's ingredient weight chart publishes 1 cup at 198 grams, which implies a density of 0.8369 grams per millilitre. That figure is below every real vegetable oil, and it is close enough to what you get from rounding 7.69 ounces (the actual cup weight in ounces) down to a flat 7 ounces and then multiplying by 28.35 grams per ounce that the arithmetic origin is visible. Whether or not that is the exact cause, the physical impossibility is enough to reject the figure. Oil is not a liquid whose density varies by measurement method the way a milled powder does — the density is a property of the substance, and the substance is well-characterised.

Related oil entries on this site cover the individual named oils. Olive oil sits at 216 grams per cup and 0.913 grams per millilitre — slightly less dense than soybean because of its higher monounsaturated fat content and slightly different molecular composition. Canola oil is at 218 grams per cup, essentially identical to soybean. Coconut oil, which King Arthur publishes at 113 grams per half cup (226 grams per cup, density 0.955), is denser than the liquid oils because it is solid at room temperature and packs more tightly; that entry is a separate case. When a recipe simply says 'oil' or 'vegetable oil' without specifying which one, the USDA figure of 218 grams per cup applies to almost any commercial cooking oil the reader is likely to have.

For recipes that specify one oil by name, use that oil's own entry. For recipes that call for a generic 'vegetable oil', use this entry. The one meaningful exception is coconut oil: because it is solid or semi-solid at room temperature depending on the season, it is not a substitute for liquid vegetable oil at equal volume even though the densities are close.

FDA regulates vegetable oils under general food safety and labelling rules rather than an ingredient-specific identity standard. The Codex Alimentarius standard CXS 210-1999 covers named vegetable oils (soybean, canola, sunflower, safflower, corn, cottonseed, peanut, palm, coconut) and specifies expected density ranges as part of the physical identification.

The category here is 'fat' rather than 'liquid' because vegetable oil behaves as a pure fat in a measuring cup: it pours cleanly, self-levels immediately, does not compact or bridge, and its density is fixed by the physical properties of the oil rather than by any handling variation. The 5 percent fat category tolerance would apply if a second accepted source existed; since King Arthur's figure is rejected, the entry is medium confidence on the strength of the USDA measurement plus corroborating Codex identity standards.