How it's calculated
kcal = grams × energy density
grams = macronutrient mass, energy density = 4 kcal/g (carbs, protein), 9 kcal/g (fat), 7 kcal/g (alcohol). Reverse: grams = kcal ÷ density. 1 kcal = 4.184 kJ.
Common values
| Nutrient | Calories per gram |
|---|---|
| Carbohydrate | 4 kcal/g |
| Protein | 4 kcal/g |
| Fat | 9 kcal/g |
| Alcohol | 7 kcal/g |
Common questions
Why is fat more than twice the calories of carbs?
Fat packs 9 kcal per gram while carbs and protein hold 4. That density is why fatty foods add up so fast.
What are Atwater factors?
They are the standard energy values the USDA and FDA use for each macronutrient, derived by Wilbur Atwater over a century ago.