Watts to METs Converter

How the watts-to-METs conversion works

A MET is a multiple of resting metabolic rate, standardised at 3.5 ml of oxygen per kilogram of body weight per minute. Power meters and ergometers report mechanical work in watts, so converting between the two requires an estimate of how much oxygen the body consumes to produce a given work rate. The ACSM metabolic equation for leg ergometry provides that bridge: VO₂ = 1.8 × work rate (kg·m/min) ÷ body mass (kg) + 7, where the +7 covers resting metabolism plus the cost of unloaded pedalling. This calculator applies the conversion as VO₂ = watts × 11.016 ÷ weight + 7, the 1.8 ml/kg·m efficiency multiplier folded into the watt conversion, then divides by 3.5 to express the result in METs.

Worked example at 150 W

A 75 kg rider holding 150 W: 150 × 11.016 = 1,652, divided by 75 gives 22.0 ml/kg/min of work-related oxygen demand. Adding the 7 ml/kg/min baseline gives a VO₂ of 29.0 ml/kg/min, and 29.0 ÷ 3.5 = 8.3 METs. At that intensity the standard MET energy relation (MET × kg × hours) implies 8.3 × 75 ≈ 622 kcal/hr. Note the direction of the weight effect: the same wattage represents a lower relative intensity for a heavier rider, because the fixed mechanical work is spread over more body mass.

A second scenario at 200 W

An 80 kg rider at 200 W: 200 × 11.016 ÷ 80 = 27.5, plus 7 gives 34.5 ml/kg/min, or 9.9 METs — roughly 789 kcal/hr at that body weight. Compare a 60 kg rider producing 100 W: 100 × 11.016 ÷ 60 + 7 = 25.4 ml/kg/min, 7.2 METs. Half the absolute power, yet nearly three-quarters of the relative intensity, because body mass sits in the denominator. This is why watts-per-kilogram, not raw watts, is the standard currency for comparing cyclists of different sizes.

What the equation assumes

The ACSM equation was validated for steady-state cycling on a stationary ergometer at work rates between roughly 50 and 200 W. Steady-state matters: during the first minutes of an effort, oxygen uptake lags behind work rate, and above the lactate threshold VO₂ drifts upward over time at a fixed wattage. Short intervals, sprints, and highly variable outdoor rides violate the steady-state assumption, and the equation loses accuracy above about 200 W where the linear efficiency relationship begins to flatten. Individual mechanical efficiency also varies — trained cyclists typically convert 20–24% of metabolic energy into pedal work, and the equation encodes a single population-average efficiency.

Why running watts are not comparable

Running power meters report a modelled quantity, not braked flywheel work. A cycle ergometer dissipates a measurable wattage; running "power" is estimated from body mass, speed, cadence, and vertical oscillation, and each vendor's model differs. The oxygen cost per watt also differs between modalities — running involves elastic energy return and eccentric muscle actions that cycling largely avoids — so feeding running watts into a leg-ergometry equation produces figures with no validated meaning. For treadmill or overground running, pace-based MET tables are the published route.

From METs to calories and back

Once an activity is expressed in METs, energy expenditure follows from MET × body mass (kg) × duration (hours). The 8.3 MET example above gives 622 kcal over a full hour for the 75 kg rider. To run that arithmetic for any MET value and duration — including values taken from published MET tables rather than a power meter — the custom MET calculator handles the general case. Working in the other direction, a MET target can be converted to a wattage: a 6 MET ceiling for a 75 kg rider corresponds to (6 × 3.5 − 7) × 75 ÷ 11.016 ≈ 95 W, which is how ergometer test protocols translate prescribed intensities into machine settings.