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A calorie is a unit of heat measurement in the metric system. It is defined as the amount of heat needed to raise one gram of pure water by 1°C under standard conditions. The term standard conditions refers to atmospheric pressure of one atmosphere and a temperature change from 15.5 to 16.5°C.

A second unit of measurement is the Calorie. The Calorie (with a capital C) is 1,000 times the size of the calorie. The difference between the two is sometimes made clear by calling the calorie the gram-calorie and the Calorie the kilocalorie. The abbreviation for the two units are cal for the gram-calorie and Cal for the kilocalorie. When you read about the number of calories contained in food or the number of calories to include in your diet each day, the term intended is the kilocalorie. It is this unit that is used by nutritionists in talking about the food value of what we eat.

Many people other than health scientists are...