卡路里（Calorie，缩写为cal），简称卡，其定义为将1克水在1大气压（101.325kPa）下提升1摄氏度所需要的热量。

由于科学家发现水在不同温度下的比热容不同，所以衍生了以下不同的定义：

≈ 0.003964 BTU

≈ 1.163×10 kWh

≈ 2.611×10 eV

≈ 0.003985 BTU

≈ 1.168×10千瓦·小时

≈ 2.624×10电子伏

≈ 0.0039671 BTU

Calories are units of energy. Various definitions exist but fall into two broad categories.

Although these units are part of the metric system, they have been superseded in the International System of Units by the joule. One small calorie is approximately 4.2 joules (so one large calorie is about 4.2 kilojoules). The factor used to convert calories to joules at a given temperature is numerically equivalent to the specific heat capacity of water expressed in joules per kelvin per gram or per kilogram. The precise conversion factor depends on the definition adopted.