The standard formula for calculating calories burned during physical activity uses MET values (Metabolic Equivalent of Task). A MET value represents the energy cost of an activity relative to resting — so MET 4 burns 4× more energy than sitting still. The formula Calories = MET × Weight (kg) × Time (hours) is used by fitness trackers, exercise physiologists, and health researchers worldwide. This page explains the formula, common MET values for popular activities, and worked examples.