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.
Calories (Kilogram,mean)
The kilogram calorie sometimes referred to as a "large calorie" or "food calorie" is the energy required to raise the temperature of one kilogram of water by one degree Celsius at one atmosphere of pressure.