What is the definition of one metabolic unit (met) and how is it measured?

The metabolic unit (met) is a measure of the energy produced per unit of surface area by a person. One met is defined as 50 kcal/h/m², which is equivalent to 18.4 Btu/h/ft² or 58.2 W/m². This unit is used to quantify the rate of heat production by the human body, which depends on factors such as muscular activity, diet, and time of day.