Calories Burned From Activity, Explained
After reading this you will be able to estimate the calories an activity burns from its MET value, your body weight and the time you spend, and you will know how wide the real error bars are.
What the calculator does and one example
The Calories Burned Calculator turns three inputs (an activity, your body weight and a duration) into an energy estimate in kilocalories. The link between them is a single number called the MET, short for metabolic equivalent of task. A MET describes how many times faster you burn energy during an activity compared with sitting still.
Here is the hook. A 70 kg person running at 8 km/h for 30 minutes burns about 280 kcal. The same person walking slowly for 30 minutes burns about 81 kcal. Same body, same clock, but the run costs roughly 3.5 times as much because running at 8 km/h is an 8-MET activity and slow walking is about 2.3 METs.
That word "about" is doing real work. The estimate is a population average. Your own number can sit 20% higher or lower depending on your fitness, the terrain and how hard you actually pushed.
What a MET means
One MET is defined as an oxygen uptake of 3.5 millilitres per kilogram of body weight per minute, which corresponds to roughly 1 kcal per kilogram per hour at rest. So a person who weighs 70 kg burns about 70 kcal in an hour of quiet sitting.
- MET
- Metabolic equivalent of task. The energy cost of an activity divided by your resting energy cost. Higher means harder.
- Resting metabolic rate
- The energy you burn at complete rest, defined as 1 MET. Everything else is measured relative to it.
- kcal
- The kilocalorie, the unit food labels call a "Calorie" with a capital C. All numbers here are kcal.
The MET scale is convenient because it is roughly independent of body weight. A 5.5 km/h brisk walk is about 3.8 METs whether you weigh 55 kg or 95 kg. Your body weight enters the calorie sum separately, because a heavier body burns more energy to move at the same MET level.
The formula and why it is shaped that way
Here m is your body weight in kilograms and t is the duration in hours. The MET value is fixed by the activity. Multiply the three and you get kilocalories.
The intuition is direct. One MET burns about 1 kcal per kilogram per hour, so a 1-MET hour for a 70 kg person is 70 kcal. Multiply by the MET number to scale up. An 8-MET activity burns eight times as fast as rest, so it costs 8 \times 70 = 560 kcal per hour, or 280 kcal in half an hour.
Notice that duration is in hours, not minutes. If you enter minutes, divide by 60 first. Thirty minutes is 0.5 hours, so an 8-MET run gives 8 \times 70 \times 0.5 = 280 kcal.
Reproducing the demo: a 30-minute run
The demo button uses the defaults: running at 8 km/h, 70 kg body weight, 30 minutes. Running at 8 km/h carries a MET of 8.0.
- Convert time to hours: t = 30 / 60 = 0.5 hours.
- Read the MET: running 8 km/h is
8.0METs. - Multiply: 8.0 \times 70 \times 0.5 = 280 kcal.
The tool reports about 280 kcal. If you double the duration to 60 minutes, the result doubles to 560 kcal, because time enters linearly. If instead you keep 30 minutes but drop to a slow walk (2.3 METs), you get 2.3 \times 70 \times 0.5 \approx 81 kcal.
How the numbers scale
Every input is linear, which makes the arithmetic easy to sanity check. Double the weight and the burn doubles. Double the time and the burn doubles. Pick an activity with twice the MET and the burn doubles. Nothing curves, nothing saturates.
The chart below shows how six activities compare for the same 70 kg person over 30 minutes. Read it as relative cost: soccer and running at 12 km/h sit near the top, yoga and slow walking near the bottom.
Because weight enters linearly, a 90 kg person burns exactly 90/70 \approx 1.29 times these numbers, so the 30-minute run becomes about 360 kcal rather than 280. The widget below lets you move weight and duration and watch the estimate track them.
Reading the result honestly
The output is a point estimate wrapped in a wide band. Treat the 280 kcal run as a range of roughly 224 to 336 kcal once you apply the 20% error the MET tables carry. That spread comes from real biology and real measurement.
- Fitness. A trained runner uses oxygen more economically at the same pace, so their real burn can sit below the table value.
- Terrain and load. Hills, wind, soft ground and a backpack all raise the cost above a flat-treadmill MET.
- Effort within a label. "Cycling, moderate" covers a wide band of paces. The MET is a midpoint, not your exact ride.
Use the estimate for comparison and planning, not for exact bookkeeping. It answers "is a swim worth more than a walk today" far better than "did I burn exactly 312 kcal".
If you want a firmer number, measure the same activity the same way each week and track the trend. The relative change is more reliable than any single absolute figure.
Common mistakes
The biggest error is confusing gross and net burn. The MET formula gives gross energy, which includes the calories you would have burned anyway just by being alive. To find the extra cost of exercising, subtract about 1 MET of resting burn.
Take the 30-minute run again. Gross is 280 kcal at 8 METs. The resting share over the same half hour is 1 \times 70 \times 0.5 = 35 kcal, so the net exercise cost is closer to 280 - 35 = 245 kcal. Most fitness apps report gross, which is why activity trackers and MET tables tend to run higher than the "extra" calories you actually spent.
Two more traps. First, entering minutes where the formula wants hours inflates the result 60 fold, so always confirm the units. Second, picking a label that flatters your effort. If you jogged but selected running at 12 km/h, the tool cannot know, and it will hand back a number that is too large.
Related tools
Calories burned pairs naturally with a few other estimates on this site. If you train by pace, the Running Pace Calculator converts speeds and predicts race times, which helps you pick the right running MET. To judge how hard an activity feels relative to your heart, the Heart Rate Zone Calculator maps effort into five zones. For aerobic fitness itself, the VO₂max Estimator gives a number closely tied to the oxygen uptake that defines a MET. And if your session is resistance work, the One-Rep Max Calculator handles the strength side that MET tables describe only crudely.
Frequently asked questions
Why do two calculators give me different calorie numbers?
They usually use different MET tables or different assumptions about resting burn. A 15% to 20% gap between two honest estimates is normal. Neither is "the truth"; both are averages.
Does a heavier person really burn more?
Yes, at the same MET. Moving more mass costs more energy. A 90 kg person burns about 1.29 times what a 70 kg person burns for the same activity and time, because weight multiplies directly in the formula.
Should I subtract these calories from my food intake?
Be careful. The tool reports gross burn, so it double counts the resting calories your body would spend anyway. If you plan intake around it, use the net figure (subtract roughly 1 MET) and expect a 20% margin.
Why is strength training so low compared with running?
MET tables measure average oxygen use across the whole session, including rest between sets. Weight training averages around 3.5 to 6 METs even though individual lifts feel intense. The metabolic cost that continues after the session (the "afterburn") is real but small, usually under 10% of the session total.
How accurate is the MET method overall?
For a group it is quite good. For one specific person on one specific day, treat it as plus or minus 20% at best. Fitness, terrain, temperature and technique all move the real figure.
Related tools
One-Rep Max Calculator
Estimate your 1RM from reps, with a %-load table.
Running Pace Calculator
Pace ↔ speed ↔ race time, plus a race predictor.
Heart Rate Zone Calculator
Five training zones from age or measured max HR.
VO₂max Estimator
Aerobic fitness from a Cooper, heart-rate or run test.
Antibiotic Resistance Evolution Simulator
Watch bacteria evolve resistance — and see why finishing the course matters.
BMI Calculator
Body mass index, WHO category and healthy weight range.