Mashed Potatoes

One US cup of mashed potatoes weighs 210 grams (7.4 ounces). Going the other way, 100 grams is about 0.48 cups.

Also called mashed potato, homemade mashed potatoes, potato mash, whipped potatoes, creamy mashed potatoes.

A cup of mashed potatoes weighs 210 g (7.4 oz). USDA weighs a cup of home-style mash at 210 g in every preparation it lists, Health Canada's 125 mL at 111 g works out to the same 210 g, and King Arthur gives 213 g. The three agree within 2%, so this entry publishes USDA's figure and King Arthur's agrees.

Mashed potatoes are boiled potatoes broken down with milk and butter, by masher, ricer or mixer. Cooking swells the starch granules inside each potato cell, and mashing breaks the flesh into a soft paste that holds small pockets of air, more of them the longer it is whipped. USDA puts milk-and-butter mash at 75.6% water, 16.8% carbohydrate and 4.2% fat.

USDA SR Legacy gives 1 cup = 210 g for home-prepared mash with whole milk and butter (FDC 168555), with whole milk only (FDC 170493), with whole milk and margarine (FDC 170037), and for mash made from dehydrated flakes with whole milk and butter (FDC 170446). The cup does not change with the fat, so USDA's figure reflects the texture of a spooned mash more than the recipe. Health Canada's Nutrient Value of Some Common Foods weighs 125 mL of homemade mash with 2% milk and margarine at 111 g, and the same for mash made from dried flakes: 0.888 g per millilitre, 210 g per US cup. King Arthur gives 1 cup at 7 1/2 oz, 213 g.

The physical check: raw potato flesh has a specific gravity of about 1.06 to 1.10, and milk and butter bring the mash down slightly, so a cup of mash with no air at all would weigh roughly 245 to 250 g. At 210 g, about one sixth of a spooned cup is air, which fits a mash that has been stirred and spooned rather than pressed.

That also explains the outliers. USDA's survey database FNDDS gives 1 cup = 250 g for mash made from fresh potatoes with milk, and the same 250 g for ready-to-heat mash and mash made from a dry mix, three foods with different water and fat: the weight of a cup with the air pressed out, assigned to all three. USDA's SR record for ready-to-eat commercial mash (FDC 169768) gives 229 g, a denser, factory-smooth product.

Retail labels for refrigerated mashed potatoes are not measurements. Bob Evans and Kroger print 1/2 cup as 140 g, which would be 280 g per cup and 1.18 g per millilitre, heavier than potato itself. Simply Potatoes prints 1/2 cup (130 g) on its US traditional mash and 2/3 cup (140 g) on its Canadian one, a serving weight set beside whichever measure is nearest. Labels are left out for that reason.

Mashed sweet potato on this site weighs 196 to 240 g per cup, because the two sources behind it describe different preparations. Instant potato flakes are a dry ingredient with their own entry: Idahoan says 1/3 cup of flakes (22 g) makes 1/2 cup of mash.

Practical guidance: use 210 g per cup of mashed potatoes, 105 g per half cup and 70 g per third of a cup, spooned into the cup and levelled without pressing. Mash pressed firmly into the cup, as for a pie topping or croquettes, can reach 240 to 250 g. For leftovers measured into a recipe such as potato bread or pancakes, weigh rather than pack.