How exercise calories are estimated: METs
Exercise scientists needed a way to compare the energy cost of activities between people of different sizes, and the unit they settled on is the MET — metabolic equivalent of task. One MET is the energy you burn sitting quietly, roughly one kilocalorie per kilogram of body weight per hour. Every activity in published tables, such as the Compendium of Physical Activities, carries a MET value that says how many times harder than rest it is: brisk walking at 3.5 mph is about 4.3 METs, running at 6 mph about 9.8. Multiply the MET value by your weight and the time, and you have an estimate of calories burned that automatically scales with body size — which is why a heavier person burns more doing exactly the same workout.
The calories burned formula
With the defaults on this page — walking at 4.3 METs, 70 kg, for one hour — the arithmetic is 4.3 × 70 × 1 = 301 kcal. Because weight sits inside the formula, the same hour of walking costs a 90 kg person about 387 kcal and a 55 kg person about 237 kcal. That is physics, not fairness: moving a larger mass takes more energy, and it is also why "the machine said 500 calories" means little without knowing whose weight the machine assumed — many assume nobody in particular and simply overstate.
Reading the activity list
The activities here span the range most people actually do. At the gentle end, yoga and stretching (3.0 METs) and brisk walking (4.3) are sustainable daily habits whose value compounds through consistency. Weight lifting, vigorous (5.0) and hiking (6.0) sit in the middle — lifting's real calorie story also includes the muscle it builds, which raises your resting burn slightly over time. Rowing (7.0), moderate cycling (8.0) and freestyle swimming (8.3) are efficient burners that spare your joints, and running at 6 mph (9.8) tops the list because it is weight-bearing, continuous and fast. Notice what the MET scale makes obvious: intensity multiplies burn per minute, but duration is yours to extend — an hour's walk you enjoy beats a twelve-minute run you dread and then skip tomorrow.
How accurate is any of this?
Honestly, approximate. MET values are averages measured across groups, and your own efficiency, fitness, speed within a label like "moderate", terrain, wind, and stop-start pauses all move the real figure — a spread of 20 percent either way would surprise nobody. Fitness trackers and gym machines have the same problem in reverse: studies regularly find them off by similar or larger margins, each in its own direction. The productive way to use any estimate is comparatively: to rank activities, to plan roughly how exercise fits a calorie budget, and to notice trends as duration or pace rises. If you are eating back exercise calories while trying to lose weight, a cautious habit is to add back only part of the estimate — the combination of optimistic burn figures and optimistic food labels is the classic reason "I burned it off" stalls.
Worked example
Walking briskly at 3.5 mph (4.3 METs), weighing 70 kg, for 60 minutes: 4.3 × 70 × (60 ÷ 60) = 4.3 × 70 × 1 = 301 kcal. The same person running at 6 mph (9.8 METs) for the same hour would burn 9.8 × 70 = 686 kcal — which is why pace changes the answer far more than small weight changes do.
How to use this calculator
- Choose your activity from the list — the MET value travels with it.
- Enter your weight in kilograms; heavier bodies burn more at the same activity.
- Enter how many minutes you spent (or plan to spend) doing it.
- Read the total calories burned in the headline panel and the per-hour rate in the stats.
- Use the duration table below the calculator to compare shorter and longer sessions at a glance.
Gross burn, net burn, and the double-counting trap
One subtlety is worth knowing: the MET formula gives your gross burn, which includes the roughly 1 MET you would have burned anyway just being alive during that hour. Your net extra burn — the calories truly attributable to the exercise — is about one MET's worth lower: for the default walk, about 301 minus 70, or roughly 231 extra kcal. This matters if you add exercise calories on top of a maintenance figure that already assumed a sedentary day: you would count that resting hour twice. In practice the error is small next to the other uncertainties, but for long, gentle activities it is proportionally the biggest, which is another reason to add back exercise calories conservatively.
It is also worth keeping exercise in proportion. An hour of brisk walking — a genuinely good workout — earns roughly the calories in a large muffin. That is not an argument against exercise, whose benefits for heart, mood, sleep, blood sugar and muscle go far beyond its calorie line; it is an argument for letting food do the heavy lifting in weight management and letting exercise make you fitter, stronger and healthier while it helps at the margins.
Important note
For information only — not medical advice. This calculator uses standard published formulas to estimate values for general education and planning. It does not diagnose, treat, or replace the advice of a doctor or other qualified health professional. If you have a health concern, are pregnant, or are making decisions about treatment, medication, or a major diet or exercise change, please talk to a healthcare professional first.