Rex says
Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.
Try a scenario
Click to load — tweak from there.Inputs
Result
Estimated speed (mph)
21.5
Speed (km/h)
34.6
Power to weight (W/kg)
2.93
Minutes per mile
2.79
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How to use this
- 1Enter sustained power (W).
- 2Enter rider weight (kg).
- 3Enter bike + kit weight (kg).
- 4Enter gradient (%).
- 5Enter aero drag area (cda).
- 6Enter rolling resistance (crr).
- 7Read your estimated speed (mph) on the right — it updates as you type.
- 8Hit Share to keep the scenario or send it to someone.
About this calculator
Cycling speed is dominated by aerodynamic drag and, on climbs, gravity. Enter your power, weight, and gradient to see the speed that physics allows.
Worked example
Using the values the calculator loads with:
Inputs
- Sustained power: 220 W
- Rider weight: 75 kg
- Bike + kit weight: 9 kg
- Gradient: 0 %
- Aero drag area (CdA): 0.32
- Rolling resistance (Crr): 0.005
Results
- Estimated speed (mph): 21.5
- Speed (km/h): 34.6
- Power to weight (W/kg): 2.93
- Minutes per mile: 2.79
What each field means
Inputs
- Sustained power (W)
- The sustained power used in the calculation, measured in W. Starts at 220 W so you have a working example on load.
- Rider weight (kg)
- The rider weight used in the calculation, measured in kg. Starts at 75 kg so you have a working example on load.
- Bike + kit weight (kg)
- The bike + kit weight used in the calculation, measured in kg. Starts at 9 kg so you have a working example on load.
- Gradient (%)
- The gradient used in the calculation, measured in %. Starts at 0 % so you have a working example on load. Accepted range: -15–20 %.
- Aero drag area (CdA)
- The aero drag area (cda) used in the calculation. Starts at 0.32 so you have a working example on load. Accepted range: 0.15–0.6.
- Rolling resistance (Crr)
- The rolling resistance (crr) used in the calculation. Starts at 0.005 so you have a working example on load. Accepted range: 0.002–0.015.
Results
- Estimated speed (mph)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Speed (km/h)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Power to weight (W/kg)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Minutes per mile
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
What CdA should I use?
0.40 upright on hoods, 0.32 in the drops, 0.25 or lower in an aero tuck on a TT bike.
Why does W/kg matter on climbs?
Above roughly 5% gradient, gravity dwarfs aero drag, so speed tracks almost linearly with watts per kilogram.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Cycling Power to Speed Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/cycling-power-speed
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/cycling-power-speed" target="_blank" rel="noopener">Cycling Power to Speed Calculator — RevenueLab</a> (2026).</p>
Source: [Cycling Power to Speed Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/cycling-power-speed) (2026).