A calorie is a unit of energy. The small calorie (cal) is the energy needed to raise 1 gram of water by 1°C. The food Calorie (Cal or kcal) is 1,000 small calories — the energy needed to raise 1 kilogram of water by 1°C. When nutrition labels say 'calories,' they mean kilocalories.

How many calories should I eat per day?

General guidelines suggest about 2,000 calories per day for adult women and 2,500 for adult men, but individual needs vary based on age, height, weight, and activity level. Active individuals may need 2,500-3,500+ calories.

What is the difference between a calorie and a kilocalorie?

One kilocalorie (kcal) = 1,000 calories (cal) = 1 food Calorie (Cal, with capital C). Nutrition labels use kilocalories but often label them simply as 'calories.' So when a label says 200 calories, it means 200 kilocalories.

What Is a Calorie? Definition, Types & Daily Requirements

Definition

A calorie is a unit of energy. There are two types:

Small calorie (cal): The energy to raise 1 gram of water by 1°C at standard pressure.
Food Calorie (Cal or kcal): The energy to raise 1 kilogram of water by 1°C. This equals 1,000 small calories.

When people say "calories" in nutrition, they always mean kilocalories (kcal).

Energy Content of Macronutrients

Macronutrient	kcal per gram	kJ per gram
Carbohydrates	4	16.7
Protein	4	16.7
Fat	9	37.7
Alcohol	7	29.3

Calorie Conversions

Unit	Equivalent
1 kcal (food Calorie)	4,184 joules
1 kcal	4.184 kJ
1 kcal	3.968 BTU
1 kcal	0.001162 kWh

Daily Calorie Needs

Group	Sedentary	Moderate	Active
Women 19-30	2,000	2,200	2,400
Women 31-50	1,800	2,000	2,200
Men 19-30	2,400	2,800	3,000
Men 31-50	2,200	2,600	2,800

Calories vs Kilojoules

Many countries (Australia, New Zealand, parts of Europe) use kilojoules (kJ) on food labels instead of, or alongside, kilocalories. To convert: kJ = kcal × 4.184. A 2,000 kcal diet equals about 8,368 kJ.

History

The calorie was first defined by Nicolas Clement in 1824. It became the standard unit for measuring food energy in the late 19th century. While the SI system prefers joules, calories remain dominant in food labeling in the Americas and much of Europe.

Convert between energy units with our energy converter.