Grams to Calories Calculator: Macronutrients to kcal

Grams to Calories Calculator

Convert macronutrient grams to food Calories

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The Atwater factors are standard values nutritionists use to estimate how many Calories (kcal) each gram of a macronutrient provides: Carbohydrates 4 kcal/g, Protein 4 kcal/g, Fat 9 kcal/g, and Alcohol 7 kcal/g.

Fat has more than double the calories per gram of carbs or protein — that's why fatty foods are so calorie-dense. Alcohol sits in between, which is why alcoholic drinks add up quickly.

Macronutrient

Grams

Calories (kcal)

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Calories

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Same Calories, Other Macronutrients

Nutrition labels list grams, but comparing food energy content really needs Calories, this calculator converts macronutrient grams to Calories using the standard Atwater factors nutritionists rely on.

How to use this grams to calories calculator

Select your Macronutrient: Carbohydrates, Protein, Fat, or Alcohol.
Enter the number of grams.
Read the calculated Calories (kcal).

What this calculator does

The Atwater factors are standard values nutritionists use to estimate how many Calories (kcal) each gram of a macronutrient provides: Carbohydrates 4 kcal/g, Protein 4 kcal/g, Fat 9 kcal/g, and Alcohol 7 kcal/g.

Calories = Grams × Atwater Factor (Carbs/Protein: 4, Fat: 9, Alcohol: 7)

Why fat is so much more calorie-dense

Fat has more than double the calories per gram of carbs or protein, that’s why fatty foods are so calorie-dense, a small amount of fat contributes disproportionately more energy than the same weight of carbohydrate or protein. Alcohol sits in between at 7 kcal/g, which is why alcoholic drinks add up in calorie count faster than their sugar content alone would suggest.

Frequently asked questions

Why does fat have more calories per gram than carbs or protein?

Fat’s Atwater factor is 9 kcal/g, more than double carbohydrates and protein’s 4 kcal/g each, this is an inherent chemical property of fat molecules, which is why fatty foods are more calorie-dense per gram.

Why does alcohol have so many calories?

Alcohol’s Atwater factor is 7 kcal/g, roughly midway between carbs/protein (4 kcal/g) and fat (9 kcal/g), which is why alcoholic drinks contribute significant calories even when they don’t contain much sugar or fat.