Calories Burned by Exercise: How the MET Formula Works

What is the MET-based calories-burned formula?

The number you read on a treadmill, the figure your watch gives you after a ride, the kilocalorie estimate inside any fitness tracker — almost all of them come from the same small piece of arithmetic. Multiply the metabolic equivalent of the activity (its MET value) by your body weight in kilograms and by the duration in hours, and you have a published estimate of the calories spent. The calories burned calculator runs exactly that formula against a catalogue of 27 common activities drawn from the 2011 Compendium of Physical Activities, the reference list maintained by the public-health research community.

A MET is the ratio of working metabolic rate to resting metabolic rate. By definition, 1 MET is the energy a healthy adult uses sitting quietly — about 1 kilocalorie per kilogram of body weight per hour, or roughly 70 kcal/h for a 70 kg person. An activity rated at 8 MET is, by definition, eight times that rate. So an 8 MET run for half an hour by an 80 kg adult costs 8 × 80 × 0.5 = 320 kcal. The elegance is that one table covers every body size: heavier bodies move more mass and burn more, lighter bodies less, and the formula scales linearly.

The catch is the word “estimate”. MET values are population averages from laboratory studies. Your real burn on a given day will land in a band around the predicted figure, and that band is wider than fitness marketing suggests. The rest of this guide explains where the numbers come from, what moves them up or down, and how to use the output without treating it as a precise count.

How calories burned during exercise are calculated

The working formula behind the calories burned calculator is a one-liner:

kcal = MET × body weight (kg) × duration (hours)

Read out loud, it says: take the activity's rated intensity, scale it to how big you are, then scale it to how long you did it. Per-hour burn is just MET times weight; per-minute burn is that divided by 60. The calculator returns all three so you can quickly project a longer or shorter session without re-typing anything.

The MET ratings themselves come from the 2011 update of the Compendium of Physical Activities, the project Barbara Ainsworth and colleagues began in 1993 and refined across two decades of indirect-calorimetry studies. The 2011 edition catalogues more than 800 activities, each measured by having subjects perform the task while researchers captured oxygen consumption with a metabolic cart. The resulting MET values are population means — the average healthy adult under controlled conditions, doing the activity at the specified intensity. The Compendium is the source the American College of Sports Medicine cites for its exercise prescriptions and is referenced in WHO physical-activity guidance.

One subtle point that catches people out: the MET formula gives gross calorie expenditure, not the “extra” calories you burned because you exercised. A 30-minute run at 320 kcal includes the roughly 35 kcal your basal metabolism would have spent over the same half-hour anyway. For most weight-tracking purposes that rounding does not matter — food databases and fitness apps work in gross calories too — but it is the reason a watch sometimes shows “active calories” and “total calories” as two different numbers. If you want only the active portion, subtract your BMR per minute (about 1.0 to 1.3 kcal) multiplied by the duration.

Worked example

Take an 80 kg adult who runs for 30 minutes at roughly 8 km/h (a steady 12-minute mile, or 7:30 per kilometre — the kind of pace where conversation is broken but not impossible). The Compendium lists running at 8 km/h as 8.0 MET. Plug the numbers in:

kcal = 8.0 × 80 kg × 0.5 h = 320 kcal

The same runner, the same day, takes a 60-minute bike commute at 16 to 19 km/h. The Compendium rates moderate cycling at 6.8 MET:

kcal = 6.8 × 80 kg × 1 h = 544 kcal

Sum for the day: 864 kcal of training, roughly a Big Mac plus small fries. Note how time matters more than intensity for total expenditure — the longer, lower-intensity bike ride burns considerably more than the harder, shorter run. This is the practical case for endurance work in a fat-loss plan; the easy hour outweighs the hard half hour. Plug other combinations into the calculator and the same arithmetic will hold — total burn rises in proportion to either MET or duration, and a 25% increase in time has the same effect as a 25% jump in intensity.

For a lighter adult the numbers shrink in proportion. A 55 kg person doing the same 30-minute run burns 8.0 × 55 × 0.5 = 220 kcal. For a heavier adult they grow. A 100 kg person burns 8.0 × 100 × 0.5 = 400 kcal. The runner pulling harder against gravity is the runner spending more fuel; the formula has no opinion about which is fair, only what is physically true.

What changes how many calories you actually burn

The MET formula gives one number. Real-world expenditure moves around that number by roughly ±10 to 15 percent for healthy adults, and further for outliers. Four factors do most of the moving.

Body weight and composition

The formula already accounts for body weight, but it assumes average body composition for the weight. A muscular 90 kg adult and a sedentary 90 kg adult are scored the same. In practice the muscular adult tends to burn slightly more — a kilogram of skeletal muscle costs about 13 kcal/day at rest, fat about 4 kcal/day — and is also usually more efficient at sustained aerobic work, which can push the actual figure either way depending on the activity. The lean body mass calculator gives you a way to track that side of things over time.

Intensity within an activity band

The Compendium splits most activities into intensity tiers precisely because effort within an activity matters. Running is not one MET value; it is 8.0 MET at 8 km/h, 9.8 at 10 km/h, 11.8 at 12 km/h. Cycling is 4.0 leisure, 6.8 moderate, 8.0 vigorous. The calculator's drop-down forces a choice because picking “running” without specifying pace would mean a 50 percent error band before any individual variation is factored in. If the session sat between two tiers, pick the closer one or average the two by hand.

Terrain, weather, equipment

Compendium values are measured indoors on level ground in thermoneutral conditions. Real exercise rarely is. Trail running with elevation gain burns 20 to 40 percent more than flat-road running at the same speed. Cycling into a headwind or up a hill can double expenditure for the same speed. Swimming open water in 16 °C sea is metabolically expensive in a way the indoor-pool figures never capture. Conversely, running on a hot day at the same pace burns slightly more because of thermoregulation; cold-weather cycling burns slightly more if you have to shiver to stay warm. For most casual estimates these effects cancel out; for athletes tracking expenditure carefully they do not.

Fitness level and movement economy

Two runners at the same speed do not always burn the same calories. The more economical runner — a more trained gait, less wasted vertical bounce, better breathing pattern — uses less oxygen for the same external work. Over a marathon, the gap between an elite and a club runner's running economy at the same pace can be 15 to 20 percent. The Compendium assumes the average untrained-to-recreational adult; very trained athletes burn slightly less than the formula predicts, very deconditioned beginners slightly more, because both are further from the average.

How to get the most out of the estimate

• Treat the number as a band, not a point. If the calculator shows 400 kcal, plan as though you burned 340 to 460. That is wide enough to absorb the everyday measurement error and tight enough to be useful for weekly weight tracking.
• Re-weigh weekly if you are using burn for a calorie target. Body weight is one of the two inputs that matter most. A four-kilogram swing changes every result by five percent and propagates straight into your deficit or surplus.
• Time your session, do not guess. The single largest source of self-reported error is overstating duration. A “45-minute” gym session usually contains 30 minutes of actual work and 15 of resting, phone-checking, and getting from one piece of kit to the next. The MET formula multiplies that error straight into the answer.
• Add daily movement to your training total. The Compendium includes everyday activities — gardening (3.8 MET), housework (3.3 MET), brisk walking (3.8 MET). Non-exercise activity thermogenesis (NEAT) is the single biggest variable in total daily energy expenditure for most people. A standing desk and a walk to buy lunch can outweigh a 30-minute workout.
• Pair the burn estimate with a maintenance target. The figure on its own is just a per-session curiosity. To convert it into a fat-loss or muscle-gain plan, layer it over a TDEE calculation and a calorie target.

Common mistakes

Picking the highest MET value to feel productive. Vigorous swimming (9.8 MET) might earn you 470 kcal for half an hour on paper, but only if you actually swam vigorous freestyle the whole time. Honest input gives a useful number; inflated input gives a worse food plan.

Counting the same calories twice. If you eat back the calories your training watch reports, then also eat back the calories the gym treadmill reports, you have double-counted the session. Pick one source for the day — usually the watch — and ignore the others.

Comparing two devices and trusting the higher one. Commercial machines tend to over-report by 10 to 30 percent; wrist-based optical heart-rate watches under-report on interval work and over-report on weights; chest-strap and lab measurements are tighter but still differ. The Compendium-based figure from this calculator is the conservative, peer-reviewed baseline; use it as the anchor and treat other readings as commentary.

Assuming exercise will out-burn a bad diet. A 70 kg adult needs roughly 70 minutes of steady 8 km/h running to burn 500 kcal — the same deficit produced by skipping a single fast-food side. Exercise protects lean mass, improves cardiovascular health, and lifts mood; it does not, for most people, drive significant fat loss without a matching dietary change.

When to talk to a coach or a doctor

For pure activity tracking, MET arithmetic is enough. For rapid weight change, training that is not producing the expected adaptations, or sudden changes in resting heart rate, fatigue, or appetite, the right next step is a professional rather than a recalculation. Thyroid disease, chronic underfuelling, REDs (relative energy deficiency in sport) in athletes, and several other conditions can shift actual expenditure well outside the ±15 percent band a healthy adult sits in. The calculator is a planning tool, not a diagnostic one.

Frequently asked questions

How accurate is a MET-based calorie estimate?

For healthy adults doing the listed activity at the listed intensity, the Compendium figures are typically accurate to within ±10 to 15 percent against gold-standard indirect calorimetry. Real-world conditions widen that band: terrain, weather, equipment, fitness level, and how honestly you logged the duration all push it. Use the result for weekly trend tracking, not for single-meal decisions.

Why does my watch show a different number?

Watches and chest straps combine heart-rate data with personalised assumptions about your VO2 max, resting heart rate, and (sometimes) lactate threshold to refine the basic MET formula. Done well, they can be more accurate than a pure MET estimate. Done poorly — or applied to activities like weights where heart rate is a noisy proxy for energy cost — they can be much worse. The Compendium-based number is the published baseline; deviations from it are not necessarily errors but they are not necessarily improvements either.

How many calories do I need to burn to lose one kilogram of fat?

A kilogram of body fat stores roughly 7,700 kcal of usable energy. Producing that deficit purely through training is slow and largely impractical; a 70 kg adult would need about 16 hours of steady 8 km/h running. The standard evidence-based plan is a 300 to 500 kcal/day combined diet-and-activity deficit, producing 0.25 to 0.5 kg per week without forcing a metabolic adaptation. The calorie calculator sets the target; the calories-burned figure tells you how much of it your training contributes.

Does the calculator handle intervals or mixed sessions?

Not directly. The cleanest workaround is to split the session by activity and run the calculator twice. For a 45-minute football game with 15 minutes of walking warm-up and 30 minutes of play, run “Soccer / football” for 30 minutes and “Walking, brisk” for 15 and add the totals. For continuous interval work (1 minute hard, 2 minutes easy), pick the MET value closest to the average across the whole session.

Why do gym machines report so many more calories?

Commercial cardio kit estimates energy expenditure from power output (watts on a bike, deck speed and incline on a treadmill) and frequently inflates the number by 10 to 30 percent. Several published comparisons against indirect calorimetry — including work by the American Council on Exercise — have shown elliptical trainers over-reporting by as much as 40 percent. Treat machine figures as motivational, not metabolic.

Should I count my BMR in the result?

The gross figure already includes the calories your body would have burned at rest during the session, so for most food-tracking purposes it is the right number. If you want the “extra” calories the workout cost you above baseline, subtract per-minute BMR (about 1.0 to 1.3 kcal, depending on body size) multiplied by the duration. The BMR calculator gives the underlying daily figure.

Does walking really burn that much?

Yes, when you walk for long enough. Brisk walking at 5.6 km/h is 3.8 MET. An 80 kg adult walking for an hour burns 3.8 × 80 = 304 kcal. Add an hour of walking five days a week and that is 1,520 kcal — equivalent to about 200 g of body fat per week, sustained, with effectively no injury risk and minimal recovery cost. It is why the WHO guideline of 150 minutes of moderate-intensity activity per week is grounded almost entirely in walking-equivalent evidence.

How does running pace change the calorie burn?

Running burn scales roughly linearly with speed across the usual range, because the work of moving body weight per unit distance is fairly constant. Doubling speed roughly doubles the kcal per minute. For training-pace planning it is often easier to think in calories per kilometre — for most adults that lands near 1 kcal per kilogram of body weight per kilometre run. The running pace calculator and the pace explainer cover the speed-and-distance side in detail.

Related calculators

• Calories Burned Calculator — the live tool that runs the MET formula across 27 activities.
• BMR Calculator — basal metabolic rate, the resting baseline this article's gross-versus-active distinction is built on.
• TDEE Calculator — total daily energy expenditure, the maintenance figure that combines BMR with everyday and training activity.
• Calorie Calculator — turn TDEE into a maintenance, cut, or bulk target.
• Protein Calculator — pair an energy plan with a protein floor to protect lean mass during a deficit.
• BMI Calculator — the quick body-mass-index reference, useful alongside any weight-management calculation.