How this works
A MET (Metabolic Equivalent of Task) is the standard way researchers and clinicians compare the energy cost of different activities. 1 MET equals the rate of energy you expend at rest, roughly 3.5 ml of oxygen per kg per minute, or about 1 kcal per kg per hour. So if an activity is rated at 8 METs, you burn 8 times more energy doing it than sitting still — which works out to 8 kcal per kg of body weight per hour. The simple formula is kcal = MET × body_weight_kg × duration_hours.
The MET values used here come from the Compendium of Physical Activities, the standard reference used by exercise physiologists and most fitness apps. They're population averages that assume a fit-but-not-elite person — your actual burn varies with intensity, fitness, body composition, and individual metabolism. Two people of the same weight running at the same pace can differ by ±15–20% in actual energy expenditure. For weight-loss planning, use this as a planning estimate, but cross-check with actual scale and tape-measure changes over weeks rather than relying on the kcal number day-to-day.
The formula
MET is the metabolic equivalent for the activity (≥ 1; sitting at rest = 1). body_weight in kg (lb × 0.4536). duration in hours (minutes / 60). The result is gross kcal — your resting burn is included. Subtract resting kcal (≈ body_weight × duration_hours) to get net activity burn if needed.
Example calculation
- 70 kg person runs at 10 km/h for 30 minutes.
- Running 10 km/h has MET 10. kcal = 10 × 70 × 0.5 = 350 kcal.
Frequently asked questions
Why does my fitness watch show a different number?
Watches use heart-rate-based estimation, not MET tables. They factor in your heart rate during the activity to refine the estimate, which can capture intensity better than a generic MET value. Heart-rate methods can be ±10–15% off; MET-based methods can be ±15–20% off. Both are estimates — neither is "right". Use whichever number is consistent for tracking trends; absolute accuracy is hard regardless.
How accurate are these numbers?
Within ±15–20% for most people. Real energy expenditure depends on intensity (a "moderate" effort varies between people), running economy, body composition, terrain, and individual metabolic factors. Use the number as a planning estimate — for instance, "I burned roughly 350 kcal so I have margin in my daily budget" — not as a precise measurement. Long-term outcomes (weight on the scale, body composition over weeks) are far more reliable than any single workout estimate.