Calories burned calculator

What a MET is

One MET is the energy cost of sitting quietly — about 3.5 millilitres of oxygen per kilogram of body weight per minute. Every activity is rated as a multiple of that. Brisk walking is roughly 5 METs, meaning five times the resting rate; running at 12 km/h is about 11.8.

The values used here come from the Compendium of Physical Activities, the reference list compiled by Ainsworth and colleagues and updated several times since 1993. It is the same source most fitness trackers and research studies work from.

The formula is straightforward: kcal/min = MET × 3.5 × kg / 200. Because body mass is in the numerator, a heavier person burns more doing exactly the same activity — moving more mass costs more energy.

Gross versus net calories

The headline figure is gross: all the energy spent during the session. But you would have burned something anyway just existing for those 45 minutes. The net figure subtracts that resting baseline, and it is the more honest number if you are adding exercise calories back into a food budget.

The gap is not trivial. For a 75 kg person doing 45 minutes at 3.5 METs, gross is about 413 kcal and net about 295 — a difference of nearly 120 kcal, which is most of a chocolate bar. Eating back gross calories is one of the quieter reasons people stall on a deficit.

How accurate is this?

Treat it as ±20-30% for an individual. MET values are population averages measured on groups of adults, and they cannot see your fitness, efficiency, technique or terrain. A trained cyclist and a beginner riding side by side at the same speed are not spending the same energy — the trained rider is usually more efficient, and burns less.

The compendium also assumes a body weight around 70 kg in its derivation, so estimates drift slightly at the extremes. And intensity within a category varies enormously: "weight training, vigorous" covers everything from a brisk circuit to long rests between heavy sets.

Where trackers disagree

Wrist-based devices estimate from heart rate and movement, which handles variable intensity better than a fixed MET does but introduces its own errors — heart rate rises with heat, caffeine, stress and dehydration without any extra energy being spent. Studies comparing consumer trackers against indirect calorimetry routinely find errors of 20-40% for energy expenditure, even where heart rate itself is accurate.

Neither method is precise enough to manage a small deficit. Both are useful for comparing sessions against each other, which is what they are actually good for.

Common questions