Free cycling VO2 max calculator that estimates aerobic capacity in mL/kg/min from your best five-minute power and body weight using the ACSM cycling equation.
Estimate your VO2 max on the bike from maximal aerobic power instead of a laboratory test. Enter the best average power you can hold for about five minutes and your body weight; the calculator converts the resulting watts per kilogram with the ACSM leg-ergometry equation. Use it to follow your own aerobic fitness across a season, because pacing, cadence and equipment all affect any field estimate.
A five-minute maximal effort is the practical field proxy for maximal aerobic power: long enough that most energy comes from aerobic metabolism, short enough to repeat in training.
It is an estimate, not a measurement. With a genuinely maximal effort and even pacing, power-based values usually land within about 5-10% of a laboratory test; gas analysis remains the only direct measurement.
Do not enter it directly. Five-minute power is typically about 1.2 times 20-minute power, so scale the value upwards first, and prefer a real five-minute test when you can do one.