How calories burned are estimated
Every activity has a MET value, a metabolic equivalent that compares its energy cost with sitting quietly. Sitting is 1 MET; running at 6 mph is about 9.8 MET. Researchers have measured hundreds of activities in the Compendium of Physical Activities. Combined with your weight and the duration, the MET value gives an estimate of the calories you burn.
The formula
Calories per minute = MET × 3.5 × weight (kg) ÷ 200
The 3.5 stands for the oxygen used at rest, in ml per kg per minute, and dividing by 200 converts oxygen into kilocalories. Multiply by the number of minutes for the total.
Worked example: a 30 minute run
A 180 lb (81.6 kg) person runs at 6 mph, 9.8 MET, for 30 minutes.
- Per minute: 9.8 × 3.5 × 81.6 ÷ 200 = 14 kcal.
- In 30 minutes: 420 kcal.
- Per hour: 840 kcal.
- Fat equivalent at 3,500 kcal per pound: about 1.9 oz.
Calories by duration (180 lb, running at 6 mph)
| Duration | Calories |
|---|---|
| 15 min | 210 |
| 30 min | 420 |
| 45 min | 630 |
| 60 min | 840 |
| 90 min | 1,260 |
Calories per hour by activity (180 lb)
| Activity | MET | kcal per hour |
|---|---|---|
| Yoga | 2.5 | 214 |
| Walking, 3 mph | 3.5 | 300 |
| Gardening | 3.8 | 326 |
| Brisk walking, 3.5 mph | 4.3 | 369 |
| Swimming laps, moderate | 5.8 | 497 |
| Hiking or vigorous weight lifting | 6.0 | 514 |
| Cycling, 12–14 mph | 8.0 | 686 |
| Running, 6 mph | 9.8 | 840 |
| Running, 7 mph | 11.0 | 943 |
Why your real number may differ
MET values are averages for adults. Fitness level, efficiency, terrain, wind and how hard you actually work all change the real figure, often by 20% or more. Fitness watches use heart rate to personalize the estimate, but they also have wide margins of error. The formula also counts the calories you would have burned anyway at rest; the extra energy from exercise is about one MET lower.
Exercise and weight loss
A pound of fat holds roughly 3,500 kcal, so burning it through exercise alone takes a lot of activity: about 4 hours of running at 6 mph for a 180 lb person. Exercise works best combined with a moderate calorie deficit from food, and it brings benefits beyond weight: heart health, mood, sleep and muscle strength. The US guidelines recommend at least 150 minutes of moderate activity a week, plus two days of strength training.