MET Values: The Hidden Table Behind Every Calorie Calculator

Every calorie-burn figure on every app and calculator descends from one idea: the MET. A metabolic equivalent of task expresses an activity’s energy cost as a multiple of resting, which turns the chaos of human movement into a tidy table. That table — the Compendium of Physical Activities, maintained by researchers since 1993 — is the engine inside this site’s burn calculator and most others. Here is how it works, how it is used, and the honest size of its error bars.

One calibration before we begin: the Compendium’s activities were measured mostly with portable oxygen apparatus on volunteers performing the task as researchers defined it. Your version of the task — your hill, your dog pulling sideways — is a remix, and the MET is the chart’s best single answer to it.

One MET, defined

One MET is the energy cost of sitting quietly: about 3.5 millilitres of oxygen per kilogram per minute, which converts to roughly 1 kilocalorie per kilogram per hour. An activity rated 4 METs costs four times that. The burn formula follows directly: kilocalories = METs × body weight in kg × hours. A 70 kg person doing a 6-MET activity for an hour burns about 420 kcal by this arithmetic — the same arithmetic our calorie burn calculator performs for fifteen activities.

Where the table comes from

The Compendium was first published in 1993 by Barbara Ainsworth and colleagues to give epidemiology a common language: instead of every study inventing its own description of ‘gardening’, researchers could code activities to standardised MET values measured in laboratory studies. It has been revised repeatedly, most comprehensively in recent editions covering hundreds of activities from archery to zumba. Its values are averages across the people measured — typically young-to-middle-aged adults of ordinary build — which is both its power and its caveat.

Where the numbers wobble

Three sources of error matter. Individual variation: your resting rate is probably not exactly 1 kcal/kg/hour — it varies with body composition, and muscular people burn more at the same labelled activity because moving costs scale imperfectly with total mass. Skill: an efficient swimmer glides at a cost a novice thrashing beside them cannot approach, yet the table gives both ‘swimming, moderate’. And intensity labelling: the difference between ‘cycling, leisure’ and ‘cycling, 19–22 km/h’ is a doubling of METs hiding inside one word’s ambiguity. Honest calculators expose the activity definitions; ours does, in the dropdown itself.

Household METs: the exercise nobody logs

The Compendium’s most subversive entries are domestic. Gardening sits around 3.8–5 METs depending on vigour; cleaning a house thoroughly, about 3.3; playing actively with children, 3.5–5.8; carrying shopping upstairs, higher still. Set against the formal exercise table, a Saturday of gardening and housework can quietly out-burn a dutiful 30-minute gym session — which reframes the entire idea of a ‘sedentary’ weekend. People who ‘never exercise’ but maintain houses, gardens, allotments and small children are often accumulating exactly the moderate-volume activity the guidelines ask for, in a currency no app counts.

This is not an argument against deliberate exercise — intensity has its own benefits — but for honesty in the ledger: if your weekends are physical, your activity factor in the TDEE calculator should say so, and your mysterious ability to maintain weight ‘without trying’ stops being mysterious.

METs at the extremes: why athletes break the table

The table’s averages strain at both ends of humanity. Very heavy individuals burn more than MET × weight implies for weight-bearing tasks, because moving costs do not scale perfectly linearly; very light, highly skilled performers burn less at the same labelled task. Elite endurance athletes are the limiting case in the other direction — their cycling or running at a pace the table prices at 16 METs may cost them measurably less per kilo, because economy is literally what training bought them. For the great middle of the population the table is a fine instrument; at the edges, treat its figures as centre-of-range and lean harder on trend data from your own body.

That is also why this site’s burn calculator presents its activities with definitions of effort — ‘19–22 km/h’ rather than ‘cycling, fast’. The MET is meaningless without the speed it was measured at, and a label that hides its definition is a number waiting to mislead.

Why METs stop at the gym door of your life

The Compendium’s blind spot is duration error: it prices activities per hour, but humans rarely perform them for the hour at the labelled intensity. The ‘hour of gardening’ includes standing with a trowel thinking; the ‘hour of swimming’ includes hanging on the lane rope; the run includes the warm-up walk. Real-world sessions average 60–75% of their nominal intensity-minutes. Honest calculators can only multiply what you give them, so the discipline sits with the entry: if your session was forty minutes of effort inside an hour of outing, enter forty. The calculator rewards honesty with accuracy; enter the outing and it will politely help you overestimate by a third.

This is also why professional guidance quotes ranges for everything in this territory. A burn figure is the centre of a distribution whose width is mostly behaviour, not biology — and behaviour, unlike biology, is yours to measure.

Using METs to plan, not to eat

The best use of a burn figure is comparison: which of two activities buys more fitness per hour of your life, and what a week of your routine adds up to. The worst use is precise repayment — eating back the exact number — because the estimate’s error band is wider than a snack. If you use exercise calories in a food budget, bank half and let the weight trend arbitrate the rest, the same discipline the BMR & TDEE page recommends.

Common mistakes

• Entering your weight wrong and blaming the table
• Choosing the most flattering activity label for what you actually did
• Eating back 100% of an estimated burn and wondering why the trend disagrees

Questions this raises

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