Activity Calorie Burn

What a MET actually is

A MET, short for metabolic equivalent of task, is the energy cost of an activity expressed as a multiple of sitting still. One MET is you at rest, and it works out to roughly one calorie per kilogram of bodyweight per hour. An activity rated at 8 METs is costing you about eight times your resting rate while you do it. Those ratings come from the Compendium of Physical Activities, first published by Barbara Ainsworth and colleagues in 1993 and revised several times since. It was built so researchers could code activity consistently across studies, which means every value is a group average measured in a lab, not a reading of your body.

A worked example

Say you weigh 180 pounds, which is about 81.6 kilograms, and you run at a moderate pace for 45 minutes. Running at that pace is rated around 8.3 METs, and 45 minutes is 0.75 hours. Multiply 8.3 by 81.6 by 0.75 and you get roughly 508 calories. Change nothing but your bodyweight and the number moves with it, because a heavier body costs more to move the same distance. That is most of what this calculator is doing.

Why your watch usually reads higher

Wrist wearables are good at heart rate and much weaker at energy expenditure. A 2017 Stanford study tested seven consumer devices and found that while most tracked heart rate closely, none estimated energy expenditure within what the researchers considered an acceptable error range. Cardio machines have the same problem for a simpler reason: many never ask your weight, so they price your session against a default person who is not you. Treat any of these as a ballpark that leans generous.

This is gross burn, not bonus burn

Here is the part almost every app quietly skips. The MET number is gross burn, meaning it includes the calories you would have spent simply existing for those 45 minutes. At 81.6 kilograms that is about 61 calories of resting metabolism sitting inside the 508, so the true extra cost of the run is closer to 447. Your daily energy expenditure already assumes you are alive and moving somewhat, so subtracting the full gross figure from your intake counts the same calories twice.

What to do with the number

I use burn estimates for comparison, not accounting. They are genuinely good at answering questions like whether a swim or a bike ride costs more for the same 40 minutes, and at helping you plan a weekly mix you will actually keep doing. What they are not good at is licensing food back, and framing training as payment for eating tends to sour both. Set your intake from your deficit target and let your daily movement be part of the activity level you already accounted for. Then judge the plan on how weight, energy, and training trend over a few weeks, which is the only feedback loop here that measures you.