The metabolic equivalent of task (MET) is a standard unit that measures the energy cost of physical activities, with 1 MET defined as the energy burned while sitting quietly (3.5 mL of oxygen per kilogram per minute). It is widely used to grade everything from vigorous household chores to running, and a free online Compendium of Physical Activities provides MET values for hundreds of tasks. While the standard "absolute" MET uses a fixed reference person for population surveys, an alternative "relative" MET is based on an individual's own resting metabolic rate, which better matches perceived exertion for athletes. Other equivalent definitions exist, such as 1 MET equaling 1 kcal per kilogram per hour or 58.2 watts per square meter of body surface area. In health and fitness studies, activity levels are often tracked in MET-hours per week, and the metric is also useful for monitoring caloric burn in dietary regimes like intermittent fasting.