Calories Burned During Exercise

What a MET is

A MET is a multiple of what your body costs at rest. One MET is sitting still. Eight METs is work that costs eight times that.

That gives one equation:

Calories per minute = METs × 3.5 × bodyweight in kg ÷ 200

3.5 is the millilitres of oxygen per kilogram per minute that one MET represents. 200 is the millilitres of oxygen in a kilocalorie. Neither is a fudge factor; both come out of what the body actually consumes.

Worked through

A 75 kg person running at 8 km/h, which is 8.3 METs, for 30 minutes:

8.3 × 3.5 × 75 ÷ 200 = 10.9 calories per minute

10.9 × 30 = 327 calories

The number your watch does not show you

That 327 includes the calories you would have spent anyway. Lying on the sofa for those thirty minutes was never free, and one MET of it is resting metabolism.

What the session actually added is everything above one MET:

(8.3 − 1) × 3.5 × 75 ÷ 200 × 30 = 287 calories

Forty calories is not much on one run. It is roughly a fifth of a long session, it compounds across a week, and it is the single most common reason a carefully tracked deficit does not produce the loss the arithmetic promised. Watches and machines almost always show the gross figure.

MET values

Work it out: the calories burned calculator runs the equation for your bodyweight and gives both the gross and the net figure.

How wrong this can be

Treat it as a range, not a reading. Two people of the same weight doing the same session can differ by twenty or thirty percent, and the same person differs day to day.

The MET values are population averages for somebody of average efficiency. A trained runner uses less oxygen at 10 km/h than an untrained one, so the fitter you get at a thing, the fewer calories it costs you to do it. Weight training is the worst fit of all: the equation assumes steady work, and lifting is short efforts with long rests, so a single number covers a session that was half standing about.

Do not eat it all back. If you are tracking a deficit, count the net figure at most, and expect the true number to be lower than the estimate rather than higher.

Common questions

Why does my watch say more?

It reports gross, it estimates your heart rate response rather than your oxygen use, and it is tuned not to disappoint you.

Does lifting burn fewer calories than cardio?

Per minute, usually yes. That is not an argument against lifting, which is doing a different job: keeping the muscle that makes the rest of the plan work.

What about the afterburn?

Real, and small. For most sessions it is tens of calories, not hundreds, and it is already inside the error bars on the number above.