Sweet potato, mashed

One US cup of sweet potato, mashed weighs between 196 and 240 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.

Mashed sweet potato is unusual on this site in that both source figures are physically correct — they describe different preparation methods of what is nominally the same ingredient.

USDA FoodData Central publishes 1 cup of cooked, boiled, mashed sweet potato at 196 grams (FDC 169305, Sweet potato, cooked, boiled, without skin), giving a density of 0.83 grams per millilitre. King Arthur's ingredient weight chart publishes 1 cup at 240 grams and 1.01 grams per millilitre. The two figures are 20 percent apart, well outside any reasonable tolerance, so we publish the range 196 to 240 grams per cup rather than a single figure.

The physics explains the disagreement. Sweet potato flesh has a real density of about 1.02 grams per millilitre — very close to water, because it is roughly 80 percent water plus dissolved sugars and starch that are denser than water. When you mash cooked sweet potato with a fork or masher, you incorporate air into the mash, and that air lowers the effective density in a measuring cup. A rough fork mash traps more air; a smooth puree traps less. USDA's 196 gram figure describes a typical home-prepared mash with substantial air incorporation. King Arthur's 240 gram figure describes a smoother preparation — a purée blended or pressed through a sieve, or the canned sweet potato commonly sold in cans alongside canned pumpkin.

For baking, the distinction matters. Recipes that specify 'canned mashed sweet potato' or 'sweet potato purée' typically expect the denser 240 gram figure, similar to how a recipe expects canned pumpkin at 245 grams per cup rather than home-cooked pumpkin at a lower weight. Recipes that specify 'freshly mashed sweet potato' or use it as a substitute for oil or eggs in quick breads typically get closer to the USDA 196 gram figure.

Sweet potato composition is close to canned pumpkin in water content (80 versus 90 percent) and behaves similarly in a batter — it adds moisture, some natural sweetness, and structure from the starch. It is not interchangeable with regular potato because the sugar content and starch structure differ meaningfully, and it is not the same as yam, which is a completely different plant with denser, drier flesh.

Related products this entry does not cover: canned yams in syrup (sold as 'candied yams' in US supermarkets), which are actually sweet potatoes in a sugar syrup and weigh differently because of the added liquid; sweet potato flour (dried and ground sweet potato flesh, weighs about 130 grams per cup and behaves like a starch); and sweet potato baby food, which is essentially the same as pureed sweet potato but sometimes with added water for smoothness.

FDA has no identity standard for mashed sweet potato specifically; sweet potatoes are covered under USDA grade standards for the whole vegetable. The Codex Alimentarius does not have a specific sweet potato standard.

The category here is 'liquid' rather than 'sugar' or 'milled' because mashed sweet potato behaves as a semi-liquid paste in a measuring cup: it settles into the container, and the density is determined by the preparation method (how much air is incorporated during mashing) rather than by scooping method. The 5 percent liquid category tolerance is exceeded here because the two source measurements describe different preparation methods, not the same product measured differently. That is why the entry publishes a range and is marked low confidence.