Calories (Kilogram,thermoc.)
The kilogram calorie (also called the large calorie, food calorie or kilocalorie) is the energy needed to warm one kilogram of water by one degree Celsius, which is 4,184 joules in the thermochemical version. It is the calorie printed on food labels.
Btu
The British Thermal Unit (Btu) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is primarily used in the United States to describe the energy content of fuels and the power of heating and cooling systems.