How do you calculate calories burned at the gym?

Through the MET system. Multiply 0.0175 by the activity's MET value, your weight in kilograms and the number of minutes. Forty-five minutes of hard weight training at 80 kg is 0.0175 × 6 × 80 × 45 = 378 kcal gross. To find what the session added rather than what your body simply spent, run the same sum with a MET of 1 — that is 63 kcal of resting cost — and subtract it, leaving 315 kcal.

What exactly is a MET?

A multiple of your resting metabolic rate, defined precisely as 3.5 millilitres of oxygen consumed per kilogram of body weight per minute. An activity rated at 6 METs demands six times the oxygen of sitting still. Since roughly 5 kcal are released per litre of oxygen, one MET works out at 0.0175 kcal per kilogram per minute, or 1.05 per hour. That last figure is worth remembering, because the shorthand everyone quotes — one MET equals one kcal per kilogram per hour — is 5% below what the definition actually gives.

Why is the net figure lower than what the machine shows?

Because the machine is counting energy you would have spent anyway. Your resting metabolism does not switch off during a workout, so the gross total includes 45 minutes of simply being alive alongside the training. At 80 kg that baseline is 63 kcal, which turns a 378 kcal gross figure into 315 kcal of genuine addition. The gap widens sharply as intensity falls: gentle stretching gives 145 gross against 82 net, an overstatement of 77%, while a hard run narrows it to 11% because the baseline is small next to the total.

How accurate is a calorie burn estimate?

Less accurate than the tidy three-digit answer suggests. MET values are averages drawn from groups of people, and individual metabolic rates vary substantially at the same body weight, so a fifth in either direction is a realistic margin before you account for fitness, technique or how hard you actually worked. Wearable devices are not obviously better; they infer effort from heart rate, which drifts with heat, caffeine, stress and sleep. Treat the number as a way to compare one session against another rather than as a measurement.

Does lifting weights burn fewer calories than cardio?

During the session, usually yes, and the reason is straightforward: much of a lifting session is spent resting between sets, so the average intensity over the whole hour is lower than it feels. Forty-five minutes of hard lifting at 80 kg adds about 315 kcal, while the same time running adds around 554. That comparison only covers the session itself, though. Resistance training is generally undertaken for what it does to strength and muscle over months, and comparing it to running purely on calories per hour measures the one thing it is least designed to do.

What about the afterburn?

It is real, and it is smaller than it is usually sold as. After hard exercise your metabolism stays somewhat elevated while your body restores oxygen stores, clears metabolites and repairs tissue, an effect known as excess post-exercise oxygen consumption. It scales with intensity and duration, so a hard interval session produces more of it than a gentle walk, but for typical training it amounts to a modest addition rather than a second workout's worth of energy. This calculator deliberately leaves it out rather than quoting a figure that varies enormously between people and sessions.

Does body weight change the number?

Directly and proportionally — it is the single biggest input after duration. The formula multiplies by your mass, so at the same activity and time a 100 kg person burns exactly two thirds more than a 60 kg person. For 45 minutes at MET 6 that is 473 kcal gross against 284, and 394 net against 237. This is simply the cost of moving a larger body, and it is also why the same session becomes gradually less expensive in calorie terms as someone loses weight.

Why do two people burn different amounts doing the same session?

Body mass explains most of it, and this calculator accounts for that. The rest comes from things no formula can see. Muscle is more metabolically active than fat, so two people at the same weight with different body composition differ. Movement economy matters — a trained lifter or runner does the same external work more efficiently, which perversely means burning slightly less. Then there is effort itself: two people can both call a session hard while doing quite different amounts of work, and a MET value cannot tell them apart.

Should I use this number to plan what I eat?

Carefully, if at all, and not as a precise figure. The error on a calorie burn estimate is wide, and the error on estimating what you eat is wider still, so treating either as exact and then subtracting one from the other compounds two uncertainties into a number with more confidence than it deserves. It is also worth knowing that the gross figure is the wrong one for this purpose, since your resting expenditure is normally already counted in whatever daily total you started from. The net figure is the one that represents an addition. This is general information rather than dietary advice, and anything specific to your health is a conversation for a doctor or a registered dietitian.

Gym Calorie Burn Calculator

Every treadmill and every fitness app will hand you a calorie number at the end of a session, and almost all of them are answering a slightly different question from the one you are asking. The figure they show is gross energy expenditure: everything your body spent during those minutes. But your bo...

YOUR SESSION

BODY WEIGHT (kg)

MINUTES

ACTIVITY — MET 6.0

MET VALUE

SESSIONS / WEEK

ADDED BY TRAINING

315 kcal

GROSS TOTAL

378 kcal

A machine would show you the gross figure. 63 kcal of it you would have burned anyway over the same 45 minutes, so it overstates the extra by 20%.

Per minute

8.4 kcal

Per hour

504 kcal

Burned anyway

63 kcal

Net in kilojoules

1,318 kJ

Net × 3 a week

945 kcal

MET used

6.0

THROUGH THE SESSION

MIN

GROSS

ANYWAY

NET

126

105

168

140

210

175

252

210

294

245

336

280

378

315

STEPS

One MET is 3.5 mL of oxygen per kg per minute, which is 0.0175 kcal per kg per minute

Gross: 0.0175 × 6.0 MET × 80.0 kg × 45 min = 378 kcal

Resting over the same time is 1 MET: 0.0175 × 1 × 80.0 × 45 = 63 kcal

Net added by the session: 378 − 63 = 315 kcal

SESSION SIMULATION

Watch the grey wedge. It fills whether you train or not — that is the cost of simply being alive for 45 minutes, and it is already inside the number on the machine. Only the gold wedge was added by the session. The whole session plays in 8.1 seconds, about 333× real time.

THE SAME 45 MINUTES SPENT DIFFERENTLY

Stretching

82 kcal

Yoga

126 kcal

Weights, easy

158 kcal

Treadmill walk

208 kcal

Elliptical

252 kcal

Weights, hard

315 kcal

Bike, moderate

365 kcal

Rowing

378 kcal

Circuit

441 kcal

Running

554 kcal

Net figures, so the resting baseline has already been taken out of every bar.

An estimate with wide error bars. MET values are population averages, and two people of the same weight doing the same session can differ by a fifth or more in either direction. Use this to compare sessions against each other rather than as a precise energy budget. Not medical or dietary advice.

Live simulation · drawn to scale · updates as you type

Created with❤️byeaglecalculator.com

HOW TO USE

1
Enter your body weight and how many minutes the session lasted. Weight matters because the whole calculation scales directly with it — a 100 kg lifter burns about 67% more than a 60 kg lifter doing exactly the same work.
2
Pick the activity that best matches what you did, or type a MET value straight in if you know one. The presets are representative published figures rather than measurements of you, which is exactly why the field is editable.
3
Read both numbers. The gross total is what a machine would show you; the figure beside it is what the session actually added once the energy you would have spent resting has been taken out. The gap between them is larger than most people expect.
4
Watch the simulation and the comparison bars. The grey wedge fills whether you train or not, and the bars re-rank the activities by what each genuinely adds over the same number of minutes.

WORKED EXAMPLE

Forty-five minutes of hard weight training, body weight 80 kg, MET 6.0. Start from the definition. One MET is 3.5 mL of oxygen per kilogram per minute, and a litre of oxygen releases about 5 kcal, so one MET costs 3.5 ÷ 1000 × 5 = 0.0175 kcal per kilogram per minute. Gross: 0.0175 × 6 × 80 × 45 = 378 kcal. That is 8.4 kcal a minute, or 504 an hour, and it is the figure a machine would display. Baseline: the same sum at 1 MET, because your body was running anyway. 0.0175 × 1 × 80 × 45 = 63 kcal. Net: 378 − 63 = 315 kcal. This is what the session genuinely added, and it is 20% below the gross figure. In kilojoules it is 1,318 kJ. Repeated three times a week it comes to 945 kcal. A note on the shorthand. Many sources give the MET equation as simply MET × kg × hours, which would make this session 6 × 80 × 0.75 = 360 kcal. That is 5% under the 378 the definition gives, because it quietly rounds 1.05 kcal per kilogram per hour down to 1.0.

THE FORMULAS

One MET, defined3.5 mL O₂ / kg / min

Energy per litre O₂≈ 5 kcal

Per kg per minute3.5 ÷ 1000 × 5 = 0.0175 kcal

Gross burnkcal = 0.0175 × MET × kg × min

Resting baselinekcal = 0.0175 × 1 × kg × min

Net from trainingnet = gross − baseline

Equivalentlynet = 0.0175 × (MET − 1) × kg × min

Per hourkcal/h = 1.05 × MET × kg

Common shorthandMET × kg × hours — runs 5% low

Kilojoules1 kcal = 4.184 kJ exactly

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Last updated: July 27, 2026 · Formula verified · MET values are population averages, so treat the result as an estimate with wide error bars · Not medical or dietary advice · Eagle-eyed accuracy for every calculation.