Calories Burned Calculator

What a MET actually is

One MET is the energy you burn sitting quietly, defined as roughly 3.5 millilitres of oxygen per kilogram of body weight per minute, or about one calorie per kilogram per hour. Every activity is then expressed as a multiple of that baseline.

Walking briskly is about 3.5 METs, so three and a half times resting. Running at a comfortable pace is around 8, cycling hard around 10, and competitive squash can exceed 12. The MET values used here come from the Compendium of Physical Activities, the reference table compiled from laboratory measurements and used throughout exercise science.

calories = MET × weight in kg × hours

Gross versus net

The headline figure is gross: everything your body used during the session, including the calories you would have burned anyway just by existing for that half hour.

For weight management the net figure matters more, because only the extra above resting is genuinely attributable to the exercise. For a 30 minute session, resting metabolism accounts for around 35 calories, so a 280 calorie run is closer to 245 of actual additional burn. Most apps quote the gross figure without saying so.

Why wearables read high

A chest strap or a wrist optical sensor measures heart rate, and heart rate is a proxy for effort rather than a measure of energy. It rises with heat, caffeine, dehydration, stress and poor sleep, none of which burn calories.

Validation studies comparing consumer devices against indirect calorimetry, the laboratory standard, have repeatedly found error rates in energy expenditure of 20% to 90%, almost always in the direction of overestimating. Heart rate itself is usually accurate; the calorie conversion built on top of it is not.

Use your device to track consistency and trends over time, which it does well. Do not treat its calorie total as a budget you can spend.

The uncomfortable arithmetic

A pound of body fat holds roughly 3,500 calories. A 30 minute run at 8 METs for a 70 kg person burns about 280. On that basis you would need around a dozen runs to lose a single pound, before accounting for the fact that appetite rises in response.

Compensation is the part that surprises people. Studies of exercise programmes consistently find that participants lose considerably less weight than the energy arithmetic predicts, because they eat somewhat more and move somewhat less for the rest of the day without noticing either.

This is not an argument against exercise. It is an argument against treating exercise as the primary lever for weight, when it is far more powerful as a lever for cardiovascular health, insulin sensitivity, bone density, mood, sleep and how long you stay independent in old age.

Where the estimate goes wrong

• Fitness level. A trained runner is more economical and burns slightly less at the same pace than an untrained one. Efficiency improves with practice, which is why the same workout stops working.
• Terrain and conditions. Hills, wind, sand, snow and heat all raise the cost substantially, and a single MET value captures none of it.
• Intensity within a category. Cycling covers everything from a flat towpath at 12 km/h to a climb at threshold. Pick the entry that matches the effort, not just the sport.
• Body composition. MET values scale with total weight, which slightly overstates the burn for people carrying more fat and understates it for more muscular ones.

How much you actually need

Public health guidance in most countries converges on 150 minutes of moderate activity a week, or 75 minutes of vigorous, plus strength work on two days. Moderate means roughly 3 to 6 METs; vigorous means above 6.

The largest health gains come from moving from nothing to something, not from something to a great deal. The curve is steepest at the start, which is worth remembering on the days when a short walk feels like all you can manage. It counts more than it looks like it does.