Cycling Power Calculator

The tool adds three resistive forces and multiplies each by speed to get watts. Rolling is mass times gravity times Crr times speed, air drag is half of air density times CdA times speed cubed, and climbing is mass times gravity times the grade fraction times speed. The three add up to the total shown.

Aerodynamic power scales with the cube of speed, so doubling your speed needs roughly eight times the power just for the air. That is why the flat-road figure jumps from about 176 watts at 30 km/h to about 381 watts at 40 km/h, with air drag accounting for almost all of the increase.

The defaults are a CdA of 0.4 square metres and a Crr of 0.005, which suit a road rider on the hoods with decent tyres. Drop the CdA toward 0.25 for a tucked aero position or a time-trial setup, and lower the Crr for supple tyres on smooth tarmac.

No. The model assumes a drivetrain efficiency of 1.0 and reports power at the wheel. Because chains and bearings lose a few percent, the power at your pedals is a little higher than the number shown, typically 2 to 3 percent more.

Climbing power depends on your total mass and the grade. In the 6 percent example a 78 kg system at 20 km/h needs about 255 watts of climbing power on its own, which dwarfs the 42 watts of air drag at that slower speed. Gravity, not the air, dominates on a steep hill.

You can set a negative gradient down to -15 percent, and the climbing term becomes negative, which lowers the total. The estimate can even reach zero or below, meaning gravity alone would sustain that speed. It does not model braking or coasting dynamics, so treat steep descents as a rough guide.

The interface uses a fixed sea-level air density of about 1.225 kg per cubic metre and assumes still air. It does not add a headwind or tailwind. At altitude the thinner air would lower drag, so the tool slightly overestimates power high in the mountains.

Switching between metric and imperial converts your speed and weights so the physics stays identical. Internally everything is computed in km/h and kilograms, then displayed in your chosen units, so the watts do not change when you flip the toggle.

No. The calculation runs entirely in your browser as you move the sliders, so nothing about your weight, speed or ride is uploaded or stored.