Calories = MET × Weight (kg) × Hours
Running (MET 9.8) for 70 kg person, 30 minutes: 9.8 × 70 × 0.5 = 343 kcal.
Metabolic Equivalent of Task — a standardized measure of the energy cost of an activity relative to resting metabolism.
No, MET-based estimates are population averages and don't adjust for individual fitness.