How To Calculate Calories Burned

A MET is a metabolic equivalent of task, a way of expressing how hard an activity is compared with sitting quietly. One MET is resting metabolism, and an activity at MET 8 costs eight times as much energy as doing nothing.

One MET corresponds to about 3.5 millilitres of oxygen per kilogram of body weight per minute. That number comes from measuring resting oxygen uptake, and it is the anchor for the whole scale.

Oxygen converts to energy at roughly five calories per litre. Multiply the oxygen uptake by five, divide by a thousand to go from millilitres to litres, and the 3.5 and the 200 in the formula fall out.

So calories per minute is MET times 3.5 times weight in kilograms, divided by 200. At MET 8 and 70 kilograms that is 9.8 calories a minute, and half an hour comes to 294.

A simpler approximation is that one MET costs about one calorie per kilogram per hour. For the same session that gives 280 against the 294 of the full formula, close enough for a quick estimate.

Body weight enters linearly. A heavier person burns more doing exactly the same work, because there is more mass to move, so a 90 kilogram walker burns about 29 percent more than a 70 kilogram one.

Duration enters linearly too. Twice the minutes is twice the calories, which is why a long slow session can out burn a short hard one.

Typical MET values give the scale a feel. Sitting is 1, walking at three miles an hour is about 3.5, cycling at a moderate pace is 8, running at ten kilometres an hour is around 9.8, and skipping rope is about 12.

MET values come from measured oxygen uptake. The Compendium of Physical Activities publishes tables of them, and every fitness tracker that reports calories is using a version of the same data.

Trackers estimate the MET rather than looking it up. They infer intensity from heart rate and motion, and studies routinely find errors of twenty to forty percent either way.

The figure is a gross number. It includes the calories you would have burned sitting on the sofa for those same thirty minutes, so the net extra is the result minus your resting rate.

That distinction matters for small numbers. A gentle walk at MET 2.5 is only 1.5 MET above rest, so sixty percent of the reported calories would have been burned anyway.

Fat mass equivalent uses the rule of thumb that a kilogram of body fat holds about 7700 calories. The 294 calorie session is therefore about 38.1818 grams of fat, if the deficit came entirely from fat, which it never does.

Cardio machines are optimistic. Treadmills and ellipticals regularly overstate by fifteen to twenty five percent, partly because they assume a fixed efficiency and partly because holding the handrails reduces the real work.

For MET 8 at 70 kilograms for 30 minutes, the answer is 294 calories, or 588 an hour, and four sessions a week comes to 1176 calories.