Cycling Speed from Power Calculator
Cycling Speed from Power — calculate it instantly for your rides, free.
Result
How it is calculated
The tool rearranges P = F × v to v = P ÷ F. P is your power in watts, F is the constant resisting force in newtons (air drag, rolling resistance and any climbing force added together), and v comes out in m/s. It is then multiplied by 3.6 to show km/h with two decimals. You provide F yourself; the tool does not calculate it from weight, CdA, grade or wind. Both inputs must be above 0. Power above 2,500 W, or a result above 150 km/h, shows no result because it is beyond any plausible steady ride. Because F is held constant, speed rises in direct proportion to power. Real air drag grows with the square of speed, so the result is only valid at the speed where you measured or estimated that force.
Worked example
You can hold 200 W and the total resisting force at your usual pace is 24 N. Speed is 200 ÷ 24 = 8.33 m/s. Multiplying by 3.6 gives 30.00 km/h. Try 300 W with the same 24 N and the tool returns 45.00 km/h, but in practice the force would climb as you speed up, so the true gain from 100 extra watts is much smaller than this.
Common mistakes
- Treating the resistance as fixed while changing the power. Air drag rises with speed, so a result far from the speed at which you estimated the force is too optimistic.
- Entering weight in kg as the resistance. The field is a force in newtons, so the number must come from the sum of drag, rolling and slope forces.
- Entering power in kJ or in W/kg. The tool wants total watts at the wheel, and it does not add drivetrain loss.
- Leaving out the slope. A climb adds a gravity force to the resistance, and if you forget it the speed will come out much too high, and above 150 km/h no result appears at all.
- Expecting a speed on a descent or with a tailwind. The force must be above 0, so a zero or negative net resistance is rejected.
About this calculator
This calculation solves the cycling power-balance equation for speed: the watts you produce must overcome aerodynamic drag (shaped by your frontal area and air density), rolling resistance from tires and road surface, and gravity on any climb, and once you add those resistances into a single total force the equation reduces to speed = power ÷ force, which gives the speed a given power output will sustain. You supply that total resisting force yourself; the calculator does not work out drag, rolling resistance or gradient for you. It is the same physics used by power-based pacing tools, just applied to answer "how fast" rather than "how many watts."
Cyclists pacing a climb, time trial or flat ride, and coaches building race strategies around a rider's known power numbers, use this to convert a target or sustainable wattage into the speed they can realistically expect, rather than relying on feel or flat-ground assumptions that fall apart once grade or wind change.
This calculator takes your power output in watts and the total resisting force in newtons (aerodynamic drag plus rolling resistance plus gravity, worked out separately) and returns the steady speed those watts will produce, in km/h.
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