Meal Calorie Calculator — calories from protein, carbs, fat and alcohol

How it works

Every calorie in a meal comes from one of four things, and each carries a different amount of energy per gram. Protein and carbohydrate give 4 kcal per gram, fat gives 9, and alcohol gives 7. Multiply the grams by the factor, add them up, and that is the meal.

The factors are the Atwater general factor system, developed at the USDA at the end of the nineteenth century and still the basis of food energy labelling. They are not arbitrary: each is a heat of combustion corrected for what the body fails to digest, absorb, or excretes as urea.

The number worth looking at is not the total, though — it is the share. Fat carries more than twice the energy of the same weight of protein or carbohydrate, so a modest-looking amount of oil, butter or cheese moves the total more than a large amount of rice does. The breakdown on this page shows which component your calories actually came from, which is usually more actionable than the total.

Worked example

For a plate with 30 g protein, 60 g carbohydrate and 20 g fat:

• Protein: 30 × 4 = 120 kcal
• Carbohydrate: 60 × 4 = 240 kcal
• Fat: 20 × 9 = 180 kcal

That is 540 kcal, or about 2,259 kJ. Note the fat: it is the smallest number of grams on the plate but supplies a third of the energy.

Add a standard drink — about 14 g of alcohol — and it contributes 14 × 7 = 98 kcal, taking the meal to 638 kcal without adding anything the body needs.

Frequently asked questions

Why is fat 9 calories a gram?

Because fat molecules are more reduced than carbohydrate or protein — chemically they hold more energy per unit of weight, and the body recovers most of it. The Atwater figure of 9 kcal/g is the heat of combustion of typical dietary fat adjusted for digestion and absorption losses. It is the reason small changes in cooking oil move a meal's calories so much.

Does alcohol really have calories?

Yes — about 7 kcal per gram, which is closer to fat than to carbohydrate. FAO's table gives a rounded 7.0, with 6.9 as the unrounded value. A standard drink containing 14 g of alcohol is therefore roughly 98 kcal before you count any sugar in the drink, which is why this page takes alcohol as a separate input.

Why don't your numbers match the food label exactly?

Labels are allowed to use more specific factors. Beyond the general system used here, there is an Atwater *specific* factor system with different values per food type, and some countries apply different treatment to fibre and sugar alcohols. Manufacturers also round. Expect a few percent of difference, not a discrepancy that matters for a meal.

Does this count fibre?

Only implicitly. In the Atwater general system, carbohydrate is measured "by difference" and includes fibre, which is counted at the same 4 kcal/g even though much of it yields less energy than that. For a very high-fibre meal, this page will read slightly high.

What share of a meal should be fat?

There is no per-meal target — the Dietary Reference Intakes give ranges across the whole day, and for adults the acceptable range for fat is 20–35% of energy. A single meal outside that range is not a problem in itself; what matters is where the day lands. The share here is shown to tell you where your calories came from, not to judge one plate.

Can I use this to work backwards from calories to grams?

Not on this page — that is the macro calculator, which takes a daily calorie target and splits it into grams of each macronutrient. This page runs the other direction: you already have the food and its grams, and want the energy. Use whichever matches what you know — the meal in front of you, or the target you're planning towards.

What does this exclude?

Everything about the food beyond its four energy-bearing components: no micronutrients, no fibre target, no assessment of food quality, and nothing about how a meal fits your overall intake. It also assumes you know the grams — which for a home-cooked meal is usually the largest source of error, well ahead of the factors themselves.