What a MET actually measures
Every activity calculator on this site converts an activity into an energy estimate using the same unit: the MET, short for metabolic equivalent of task. One MET is defined as the rate of energy expenditure at rest, conventionally taken as 3.5 mL of oxygen consumed per kilogram of body weight per minute, which corresponds to roughly 1 kcal per kilogram of body weight per hour. A 4-MET activity therefore costs about four times the resting rate.
The assignment of MET values to specific activities comes from the Compendium of Physical Activities, a public reference maintained for research use that codes hundreds of activities with a MET value and an intensity category (light, moderate, vigorous). The codes are the standard input for population studies of physical activity energy expenditure, and they are the standard input for our calculators too. When you see "walking, 3.5 mph, MET 4.3" on one of our tool pages, that value comes from the compendium, not from an estimate we invented.
The formula, in one line
Energy in kcal = MET value × body weight in kg × duration in hours. The multiplication is the entire calculation. A worked example: walking at 3.5 mph has a compendium MET value of 4.3. For a 70 kg person walking for 30 minutes (0.5 hours), the estimate is 4.3 × 70 × 0.5 = 150.5 kcal. Change any of the three inputs and the output scales linearly: double the duration, double the estimate; a 90 kg person spends about 29% more than a 70 kg person on the same activity.
Weight in kilograms is essential because the MET definition is per kilogram. If you work in pounds, convert first: divide pounds by 2.20462, or use our kg to stone conversion calculator for the stone step.
Why the same activity has multiple MET values
The compendium does not assign one number to "cycling" or "gardening". It assigns numbers to specific efforts: "cycling, 12-13.9 mph, light effort" is one code; "cycling, 16-19 mph, racing" is another, with a much higher MET value. The distinction that matters most is between the effort you perform and the effort the activity usually involves. Carrying a load, going uphill, or working at a faster cadence moves you to a higher code; a leisurely pace moves you down.
Our activity calculators therefore ask for the intensity or the specific variant rather than giving a single site-wide number per activity. The yoga calories for beginners calculator uses a beginner-pace code, the burpees vigorous intensity calculator uses a vigorous code, and the mopping calories burned calculator uses a household-activity code. Each tool page states which compendium entry it uses, so the arithmetic is auditable.
Gross versus net energy: the common confusion
The MET formula above gives gross energy expenditure: the total burned during the activity, including what you would have burned sitting anyway. Some studies report net expenditure, which subtracts the resting component (1 MET × weight × duration) from the gross figure. In the 30-minute walking example, the resting component is 1 × 70 × 0.5 = 35 kcal, so the net value would be 150.5 − 35 = 115.5 kcal. Both conventions exist in the literature. All of our calculators report gross values and label them as such, because gross values are what the compendium's activity codes multiply into directly.
Limits of MET-based estimates
MET values are population averages measured under laboratory conditions. They do not capture individual differences in walking efficiency, fitness, terrain, weather, or clothing. Real expenditure on a hilly route can exceed the compendium estimate for the nominal speed, while a very efficient mover may fall below it. For interval activities, the correct approach is to compute each segment at its own MET value and sum, rather than averaging the MET codes. The estimate is a reasonable arithmetic expectation, not a measurement of any individual session.
Try the method on our activity tools
- Walking calories per 30 minutes - the worked example above, adjustable for weight and pace.
- Yoga calories for beginners - beginner-pace compendium code.
- Burpees calories, vigorous intensity - a vigorous-code example.
- Mopping calories burned - household activity codes.
For the full list of data sources and how each calculator selects its code, see the methodology page. As with every estimate on this site, results are general arithmetic for information purposes only - see the disclaimer.
Choosing the right code in practice
The talk test is the simplest rule of thumb that matches the compendium's own intensity bands. During a light activity you can hold a conversation comfortably and sing without pausing; during a moderate activity you can talk but not sing; during a vigorous activity you can say only a few words before needing a breath. Those three bands map onto the light, moderate, and vigorous code families the compendium defines, and they are the bands our tool pages use when they ask you to pick a pace. If you are genuinely unsure between two codes, compute both and read the result as a range rather than a point value - the honest output of a MET-based estimate is a band of roughly 15-25% around the central number, not a single figure.
One more practical note: the compendium reports values for the activity as performed, including rest built into the session. A 30-minute circuit class that includes water breaks still uses the circuit code for the full 30 minutes, because the code was measured that way. Splitting hairs over the exact rest fraction changes the estimate far less than picking the wrong intensity band does.