Aerobic Power Output Calculator
Aerobic power output converts your VO2max measurement into mechanical watts, giving cyclists and endurance athletes a physiologically grounded power ceiling. This calculator uses the ACSM standard of 20.9 kJ per litre of oxygen consumed and a user-adjustable gross mechanical efficiency to estimate power at VO2max and approximate functional threshold power.
Aerobic power formula (ACSM)
VO2max (L/min) = VO2max (mL/kg/min) x body mass (kg) / 1000
Power at VO2max (W) = VO2max (L/min) x 20,900 J/L x efficiency / 60 s
Estimated FTP (W) = power at VO2max x (FTP% / 100)
20,900 J/L is the energy equivalent of 1 litre of O2 at a respiratory exchange ratio of approximately 0.96 (mixed fuels), as used in ACSM metabolic standards.
Understanding aerobic power
- VO2max above 60 mL/kg/min is considered high for recreational athletes; elite endurance athletes typically exceed 70 mL/kg/min.
- Increasing gross mechanical efficiency through training allows more watts for the same VO2.
- FTP typically sits at 70-80 percent of power at VO2max for well-trained cyclists.
- Relative power at VO2max (W/kg) is a strong predictor of endurance race performance on hills.
Aerobic power output: frequently asked questions
What is aerobic power output?
Aerobic power output is the mechanical power produced using oxygen-dependent energy systems, expressed in watts. It is directly related to VO2max: a higher VO2max allows a greater aerobic power output. At VO2max, approximately 75-85 percent of that power can be sustained for 40-60 minutes (the functional threshold power).
How is aerobic power calculated from VO2max?
The relationship is: Power at VO2max (W) = VO2max (mL/kg/min) x body mass (kg) x 0.001 x 20,900 / 60 x gross mechanical efficiency. Using a gross efficiency of approximately 25 percent for cycling: Power (W) = VO2max (L/min) x 20,900 x 0.25 / 60.
What is the energy equivalent of one litre of oxygen?
The energy equivalent of oxygen is approximately 20.9 kJ per litre (based on a mixed substrate combustion ratio, close to 20.1 kJ/L for fat and 21.1 kJ/L for carbohydrate). This value is published by the ACSM and used in standard metabolic calculations.
What is gross mechanical efficiency in exercise?
Gross mechanical efficiency (GME) is the ratio of mechanical work output to total metabolic energy input, expressed as a percentage. For cycling, GME is typically 20-25 percent. For running, the concept is expressed as running economy (O2 cost per km). This calculator uses a default of 25 percent for cycling.
How does aerobic power relate to FTP?
Functional threshold power (FTP) is approximately 70-80 percent of power at VO2max for trained cyclists. Elite athletes sustain a higher fraction of VO2max at threshold. The Coggan power zones use FTP as the reference point for all training intensity zones.
Official sources
- American College of Sports Medicine (ACSM). ACSM's Guidelines for Exercise Testing and Prescription, 11th ed. (2022). Lippincott Williams and Wilkins. ACSM Guidelines.
- Joyner MJ, Coyle EF (2008). Endurance exercise performance: the physiology of champions. Journal of Physiology, 586(1), 35-44. PubMed 17901124.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.