Cycling Power (VO2max → sustainable power) calculator

What it does

The Cycling Power calculator estimates the sustainable bike power you can hold for a given duration, derived from your VO2max, gross efficiency, body mass, and the fraction of VO2max you can hold for that duration. It is a physiological estimator — useful when you don't have a recent CP/W' or FTP test but do know (or can reasonably guess) your VO2max.

It is NOT a race-split projector. For "given my CP, CdA, course profile, and conditions, what's my bike split?" use the race planning wizard step 2 which runs the bike split physics directly.

URL: /calculators/ then open Cycling Power. Direct path: /static/calculators/cycling_power_calculator.html.

Inputs the form asks for

• Gender (select).
• Duration (select: presets like 5 min, 20 min, 60 min, or Custom; Custom unlocks the Custom Duration seconds field).
• Custom Duration (seconds) — only when Duration is set to Custom (default 1200 = 20 min).
• Body Mass (kg) — default 75; range 30-200.
• VO2max (mL/kg/min) — default 55; range 15-100.
• Gross Efficiency (%) — default 20; range 10-30.
• Fraction of VO2max (%) — default 85; range 50-120. The share of VO2max you can sustain for the chosen duration (higher for short efforts, lower for long).
• RER (Respiratory Exchange Ratio) — default 0.95; range 0.70-1.10. Affects the energy-per-litre-O2 substrate factor.
• Show Uncertainty Band (checkbox) — toggle a ±band around the central estimate.
• 20-min Power calibration (optional) — if you enter a recent 20-min average power, the calculator back-solves a personalised efficiency value rather than using the population default.

None of the inputs are flagged required by the form; sensible defaults populate every field so the calculator returns a number immediately, then you can edit your own values.

Outputs

• Estimated power (W) for the chosen duration.
• W/kg (power-to-weight).
• Efficiency used in the calc — either the value you entered or, if you supplied a 20-min calibration, the personalised back-solved efficiency.
• Uncertainty band (low / high) when the toggle is on.
• Coggan zone table showing where the estimated power sits on a standard 7-zone scale.

When to use it

• You don't have a recent CP/W' test (run the Critical Power calculator if you do).
• You have a lab VO2max number and want a sanity check on your field power.
• You want to compare across athletes at the same VO2max and see how efficiency, mass, or RER shift sustainable power.

When NOT to use it

• For predicting a specific race time on a specific course — use the race planning wizard which models drag, climbing, and conditions.
• If you don't know VO2max — the estimate is dominated by it. Run a CP test instead.

Common gotchas

• Fraction of VO2max is the biggest knob most users get wrong. As a rough guide: 100-110% for ~5 min, 90% for ~20 min, 80% for ~60 min, 70% for ~3 h. Coaches tune this from athlete history.
• Gross efficiency at 20% is a population average. Trained cyclists are often 22-24%. Use the 20-min calibration to personalise.
• Body mass matters for W/kg but doesn't affect raw watts — if you only care about W, leave it at default.

See also: Critical Power calculator, Yousuli bike zones.