Illustrated Glossary of Organic Chemistry

Calorie (cal; small calorie): An energy unit equal to the approximate amount of energy required to raise one gram of water by one degree Celsius, or about 4.2 joules. (The unit is only approximate because the heat capacity of water varies with the temperature of the water.) The calorie is not part of the International System of Units, but is still widely used. Not to be confused with a food calorie (large calorie), which is equal to one kilocalorie.

Raising the temperature of one liter of water from 20 oC (about room temperature) to 100 oC (water's boiling point) requires approximately (1000 grams x 80 oC) = 80,000 calories (80 kcal).

This meatball sandwich has about 480 large calories.