How many calories are in oatmeal, dry vs cooked?

The numbers

USDA FoodData Central carries separate entries for dry and cooked oats. Dry, unfortified oats are about ≈379 calories per 100g, with about ≈13.2g protein, ≈6.5g fat, ≈67.7g carbohydrate and ≈10.1g fiber. Cooked in water without salt, the same oats measure about ≈71 calories per 100g, with about ≈2.5g protein, ≈1.5g fat and ≈12g carbohydrate.

Oats	Dry, per 100g	Cooked, per 100g
Calories	≈379	≈71
Protein	≈13.2g	≈2.5g
Fat	≈6.5g	≈1.5g
Carbohydrate	≈67.7g	≈12g

Why the drop is bigger than pasta or rice

Dividing the dry figure by the cooked one gives about 5.3 (379 ÷ 71). That is a much bigger drop than cooked vs dry pasta, where the ratio is only about 2.3. The reason is how each food is cooked. Pasta is boiled in a full pot of water, then drained, so most of that water never ends up on the plate. Oats are simmered in just enough liquid to be absorbed, and almost none of it is poured off. The calories in the oats stay the same the whole time; the water just makes up a bigger share of every spoonful once it has been cooked and left in the bowl.

Dry half-cup vs a cooked cup

Most people scoop oats by the half-cup, not the gram. USDA's own portion data puts a cup of dry oats at about ≈81g, so a half-cup is close to ≈40g — about ≈152 calories. That nearly matches the FDA's own reference amount for plain, unsweetened dry hot cereal, which is 40g, set out in its food-labelling rules.

Cook that 40g in water and the calories stay at about ≈152, but the weight changes: at the ≈71-per-100g cooked figure, 40g of dry oats becomes close to ≈214g of porridge. A full measured cup of cooked oatmeal (≈234g) works out closer to ≈166 calories, a touch more than the half-cup dry serving, because it holds slightly more oats depending on how much water you use and how thick you like it. Treat "a cup of oatmeal" as a rough guide, not a fixed gram count.

What toppings add

USDA's ≈71-per-100g cooked figure is for oats simmered in plain water. Everything added after that sits on top of it:

• Whole milk instead of water: about ≈74 calories for a half-cup (122g).
• A medium banana: about ≈105 calories (118g).
• A tablespoon of peanut butter: about ≈96 calories (16g).
• A tablespoon of honey: about ≈64 calories (21g).

Put a few together and the total climbs fast. A half-cup of dry oats (≈152 calories), cooked with water, topped with milk and a banana, comes to roughly ≈331 calories, more than double the oats on their own. See oats and oatmeal for the full USDA breakdown, and peanut butter for more topping numbers.

Common mistakes

• Comparing the plain cooked-oatmeal number to a bowl made with milk, fruit or sugar. USDA's ≈71-per-100g figure assumes water only.
• Treating a cooked "cup" as a fixed amount of dry oats. It moves with how much water you add and how long you cook it.
• Measuring dry oats by a cup that compresses. A scale removes the guesswork that packing a half-cup can add.

What to do instead

• Weigh dry oats before cooking. About ≈40g is close to a half-cup and to the FDA's own reference serving, so it is a steady unit to track.
• Log the cooking water as zero calories, then add milk, fruit, nut butter or sweetener separately, since none of that is in the plain oats figure.
• Check how a bowl fits your day with the macro calculator, and read about the fiber in oats, especially beta-glucan, on Harvard's Nutrition Source if you want the full picture beyond calories.