Calories Burned Calculator

How the estimate is made

Most calorie burn estimates use MET values, metabolic equivalents, where one MET is the energy cost of sitting quietly, defined as 3.5 millilitres of oxygen per kilogram per minute.

An activity with a MET value of 8 costs eight times resting expenditure. Calories burned equals MET times weight in kilograms times duration in hours.

The MET values come from the Compendium of Physical Activities, a published reference that assigns values to hundreds of activities based on measured oxygen consumption. It is the standard source and it is an average across the people who were measured.

Why the estimate is rough

MET values are population averages and individual variation is substantial. Efficiency of movement, training status, terrain, technique and body composition all affect the actual cost.

A trained runner is more economical than an untrained one at the same pace, so burns fewer calories for the same distance. That is the opposite of what most people assume.

The compendium's own documentation notes that values are approximate and intended for population-level work rather than individual prescription. Errors of 20% to 30% for an individual are entirely plausible.

Gross against net

Most calculators report gross calories burned, which includes the resting metabolism that would have occurred anyway.

The additional expenditure from the activity is the net figure: gross minus what you would have burned sitting still for the same period. For an hour of moderate activity that difference is 60 to 90 calories.

It matters when calories burned are being eaten back, because using the gross figure double-counts the resting portion that is already in the daily maintenance estimate. That is a small error and it compounds daily.

The afterburn, kept in proportion

Excess post-exercise oxygen consumption, the elevated metabolic rate after training, is real and is routinely overstated.

For moderate exercise it amounts to a few percent of the session's cost, perhaps 10 to 30 calories. For very high intensity work it is larger, and still typically under 10% of the session.

Claims that a session continues burning hundreds of calories for a day afterwards are not supported. The main energy benefit of exercise is the energy used during it, plus the lean mass that resistance training preserves.

Why exercise disappoints for weight loss

Exercise burns less than people expect and increases appetite by an amount that frequently offsets much of it. There is also compensatory reduction in non-exercise activity: someone who trains hard in the morning often moves less for the rest of the day, unconsciously.

The trial evidence is consistent: exercise alone produces modest weight loss, and exercise combined with dietary change produces considerably more than either.

None of which is an argument against exercise, which improves cardiovascular health, insulin sensitivity, mood, sleep, bone density and mortality risk regardless of what happens to weight. It is an argument against treating the calorie figure as the reason to do it.

The one place these estimates earn their keep is comparison rather than accounting. If a MET-based figure says a 40 minute swim costs roughly what a 60 minute walk costs, that relationship is likely to be about right even where both absolute numbers are out by a quarter. Using the calculation to choose between activities, or to see whether an intended change in routine is meaningful at all, is a use the underlying data can support. Using it to decide what to eat afterwards is not.