Calorie is an energy unit, which is still widely used in nutrition measurement and fitness manual. The international standard unit of energy is joule. Generally speaking, calories can be divided into two types:

Calories, also known as capital letter C, are most commonly used in food labels, which is equivalent to the heat required to raise 1 0,000 grams of water from 1 4.5 degrees Celsius to 15.5 degrees Celsius at1atmospheric pressure, which is about equal to the internal energy of 4 186 joules.

Small card, also known as cal, is common in scientific research literature, 1000 small card = 1 big card.