A worked example
300 g of raw chicken at 130 kcal per 100 g weighs 225 g after roasting. The batch still holds 390 kcal, so the cooked meat is 173 kcal per 100 g and a 150 g portion is 260 kcal.
Why cooked food has more calories per 100 g
Heat drives water out. The protein, fat and carbohydrate stay put, so the same calories now sit in fewer grams. Meat usually keeps 65 to 80% of its raw weight. Rice and pasta go the other way and roughly double or triple, because they soak water up, so their cooked figure per 100 g drops.
That’s why a food table lists both “raw” and “cooked” entries, and why logging cooked chicken against the raw figure undercounts it by a quarter or so.
How much common foods change
Grains and pulses soak up water, so they roughly double or triple; meat loses water and fat, so it shrinks by a quarter or more. The last column is what 100 g raw usually weighs once cooked, so you can use it the other way round too: 250 g of cooked rice started out as about 90 g dry.
| Food | Raw, kcal per 100 g | Cooked, kcal per 100 g | 100 g raw becomes |
|---|---|---|---|
| White rice | 360 | 130 | 277 g |
| Pasta | 371 | 158 | 235 g |
| Porridge oats | 379 | 71 | 534 g |
| Lentils | 352 | 116 | 303 g |
| Potatoes, boiled | 77 | 87 | 89 g |
| Chicken breast | 120 | 165 | 73 g |
| Beef mince, 20% fat | 254 | 272 | 70 g |
What to count as added
Anything that stays in the food: oil, butter, a marinade that cooks on. Oil left in the pan and fat you pour off didn’t make it to the plate, so the true total is a little lower than the figure here. Weighing the whole batch is what makes this work, so weigh the same food you started with.
Questions people ask
Should I log food raw or cooked?
Either, as long as the figure matches the state you weighed it in. Raw is more consistent if you can weigh before cooking. This page is for when you can’t, or when you cook a batch and eat it over days.
How much weight does meat lose when cooked?
Usually a fifth to a third, depending on the cut, the heat and how long it cooks. Weigh your own batch once and you’ll know your number.
What about a dish with lots of ingredients?
Use the recipe calculator. It adds up every ingredient and works out the same per 100 g figure for the finished dish.