Calories vs. Kilograms: Energy vs. Mass

A kilogram (kg) is a unit of mass; a calorie (cal) or kilocalorie (kcal) is a unit of energy. They measure fundamentally different physical quantities and cannot be directly converted.

1 kcal = 1,000 cal (the “Calorie” on food labels is actually a kcal).

Energy content of body tissue is often estimated: ~7,700 kcal per kg of adipose tissue (fat), but this is an approximation for weight-loss modeling, not a physical equivalence.