🚴Cycling Power Calculator

About this tool

Choose whether you know your speed or your power, then enter rider and bike weight, gradient, headwind, riding position, tyres and surface, altitude and temperature, in metric or imperial units. The tool gives the watts (or speed), watts per kilogram, kilojoules per hour and a breakdown of the power spent on air resistance, climbing and rolling resistance. Nothing is stored.

The physics of cycling power

To keep moving at a steady speed, a rider must overcome three forces. Rolling resistance is Crr × weight, roughly 0.004 for good road tyres and higher on gravel or trails. Gravity is weight × gradient on climbs. Aerodynamic drag is ½ × air density × CdA × speed², where CdA is drag area, about 0.40 m² sitting upright, 0.32 on the hoods and 0.23 on aero bars. Power is force × speed, plus about 3% lost in the drivetrain. Because drag grows with the square of speed and power with the cube, going faster on the flat gets expensive quickly. In the example, a 75 kg rider on a 9 kg bike on the hoods needs about 143 W for 30 km/h, around 80% of it fighting the air, while 200 W gets them to about 34 km/h. On a 6% climb at 15 km/h, gravity takes almost 90% of the effort, so watts per kilogram, not raw watts, decides who climbs fastest. Thinner air at altitude reduces drag, and a headwind adds to the air speed you push against. A rough energy rule: kilojoules of work roughly equal the food calories burned, because the body is about 20–25% efficient. Honest limits: CdA and Crr vary between riders, bikes and roads, so treat results as estimates. A power meter gives real numbers. The pace calculator, the calories burned calculator and the VO2 max calculator are related.

Frequently asked questions