Mets to Watts Calculator: Formula and Examples

A METs-to-watts calculator estimates the mechanical power of an activity from its metabolic equivalent (MET) value and your body mass. Enter METs and weight in kilograms, and it returns estimated watts; the result is an approximation, not a direct measurement of exercise-machine output.

Formula

The calculator uses the conventional MET-based estimate for oxygen consumption and converts that oxygen use into an approximate energy rate:

Estimated power (W) = METs × 3.5 × body mass (kg) ÷ 200

• METs is the activity’s intensity expressed as a multiple of resting oxygen use; it has no physical unit.
• Body mass is entered in kilograms (kg).
• Estimated power is expressed in watts (W), where one watt is one joule per second.

The calculation treats one MET as oxygen consumption of 3.5 millilitres per kilogram per minute. It assumes roughly 5 kilocalories are released for each litre of oxygen consumed. The same calculation therefore gives an estimated energy rate in kilocalories per minute (kcal/min). The watt figure is that estimated metabolic energy rate converted to joules per second; it is not necessarily the external mechanical work delivered to a pedal or other device.

Worked Example

Using the calculator’s default values—6 METs and a body mass of 70 kg:

1. Estimate oxygen use: 6 × 3.5 × 70 = 1,470 millilitres per minute, or 1.47 litres per minute.
2. Estimate energy use: 1.47 × 5 = 7.35 kcal/min.
3. Convert the energy rate to watts: 7.35 × 4,184 ÷ 60 = 512.54 W.
4. Round to the calculator’s zero decimal places: 513 W.

The calculator’s formula gives 6 × 3.5 × 70 ÷ 200 = 7.35 kcal/min; converting that rate yields approximately 512.54 W, which rounds to the same displayed answer, 513 W. The displayed energy-rate helper is 7.35 kcal/min.

What METs and watts mean

A MET is a way to describe activity intensity relative to a conventional resting reference. An activity rated at 6 METs is estimated to require six times that reference level of oxygen use per kilogram of body mass. MET values are often assigned to activities using population reference tables, so a listed value is an estimate rather than a personal measurement.

Watts describe power: how quickly energy is transferred or used. On an exercise bike, a machine’s watt reading commonly represents mechanical power at the pedals, determined from its measurements or internal model. The MET-based number above instead estimates whole-body metabolic energy expenditure. Human muscles are not perfectly efficient, and the body uses energy for functions beyond the external work, so these two kinds of watts should not be treated as interchangeable.

How to use the estimate

Choose a MET value that reasonably represents the activity and enter body mass in kilograms. For example, a broad activity category may have a reference MET value, but pace, terrain, technique, fitness, and individual physiology can all change actual effort. A calculator can apply the arithmetic consistently; it cannot determine your exact oxygen consumption from the activity name alone.

• Use a MET value from a clearly described activity and intensity, rather than choosing a number solely because it produces a desired result.
• Convert body mass before entering it. For pounds, divide by 2.20462 to get kilograms; for example, 154 lb is about 69.9 kg.
• Read the result as estimated metabolic power in watts. Keep the separate kcal/min figure if your goal is understanding estimated energy use.
• Keep precision in perspective: the rounded output does not mean the underlying estimate is accurate to the nearest watt.

For a rough US-customary cross-check, 1 kg equals about 2.20462 lb and 1 W equals about 0.001341 horsepower. These conversions change units, not the assumptions behind the estimate. The calculator accepts kilograms so that body mass matches the standard MET formula.

Common mistakes and limits

The most common input error is entering pounds as if they were kilograms. Since body mass is multiplied directly into the formula, that mistake can make the result more than twice as large. Another frequent misunderstanding is comparing this estimate directly with a bike’s displayed watts. A measured mechanical-power value and estimated metabolic power refer to different quantities.

• MET values are approximate: reference values describe typical energy demands, not a guaranteed personal response.
• One MET is a convention: resting oxygen use varies among people, so 3.5 ml/kg/min is not exact for everyone.
• Oxygen-to-energy conversion is simplified: the energy released per litre of oxygen depends partly on the mix of fuels being used.
• Rounding hides uncertainty: displaying a whole watt is a formatting choice, not proof of measurement precision.

For a more individualized estimate, measured oxygen consumption is more informative than assigning a general activity MET. For external cycling power, use a device or method designed to measure or estimate mechanical watts. Neither alternative makes the simple MET calculation a direct measurement of all forms of exercise output.

Frequently Asked Questions

How do I convert METs to watts?
Multiply METs by 3.5 and body mass in kilograms, then divide by 200: W ≈ METs × 3.5 × kg ÷ 200. This estimates metabolic power under the standard assumptions described above.

Can I convert METs to watts without body weight?
Not with this formula. Body mass is required because the conventional oxygen-use estimate is expressed per kilogram. Without it, you can describe the activity’s intensity in METs but cannot calculate this person-specific watt estimate.

Are MET watts the same as watts on an exercise bike?
No. MET-derived watts estimate metabolic energy use by the body, while an exercise bike’s watt figure generally describes external mechanical power. The values can differ substantially.

How many watts is 1 MET?
It depends on body mass. With this formula, 1 MET is about 1.225 W per kilogram; for a 70 kg person, that is about 85.8 W. It remains an estimate based on the conventional resting MET definition.

Can I enter my weight in pounds?
Convert pounds to kilograms first by dividing by 2.20462. For instance, 180 lb is about 81.6 kg. Entering 180 directly into the kilogram field would produce an incorrect, much higher estimate.

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in mets | Activity intensity | METs | 6 | 0
in kg | Body mass | kg | 70 | 0
out watts | Estimated power | W | mets * 3.5 * kg / 200 | 0
out kcalmin | Estimated energy use | kcal/min | mets * 3.5 * kg / 200 | 2