Bike Power
Calculator.
Work out the watts you need to hold a given speed. Enter your weight, speed, gradient, position and surface to see total power, watts per kg and exactly where every watt is going.
Results update as you type. Figures assume sea level air density (1.225 kg/m³) and 97.5% drivetrain efficiency.
How the calculator works
Every watt you push goes into beating one of three forces. Add them up, multiply by your speed, then divide by drivetrain efficiency, and you have the power at the pedals.
Watch the breakdown as you change the gradient. On the flat, aero drag is usually 75 to 85% of your total power, which is why position and clothing beat a lighter frame. Past about 6%, gravity takes over and weight is king.
Bike power FAQ
A recreational rider holds roughly 100 to 150 watts on the flat, a fit club rider 200 to 250 watts for an hour, and a domestic professional 300 to 400 watts. Because power needed rises with the cube of speed, going from 18 to 22 mph on the flat can cost you close to 80 extra watts.
Power is the sum of three forces multiplied by your speed, then divided by drivetrain efficiency. Gravity power is mass times gravity times the gradient. Rolling resistance is mass times gravity times the rolling coefficient. Aerodynamic drag is half the air density times your CdA times air speed squared. Aero dominates on the flat, gravity dominates on climbs.
CdA is your drag coefficient multiplied by your frontal area, in square metres. On the hoods a typical road rider is around 0.40, in the drops 0.32, and on aero bars 0.27. Since aero drag scales with speed squared and aero power with speed cubed, dropping your CdA from 0.40 to 0.32 at 22 mph saves roughly 35 watts for free.
Watts per kilogram at threshold is the standard fitness yardstick. Under 2.5 W/kg is a beginner, 2.5 to 3.5 is a regular recreational rider, 3.5 to 4.5 is a strong club racer, and above 5.0 puts you in elite amateur territory. It matters most on climbs, where you are fighting your own body weight.
On the flat, barely. Rolling resistance scales with weight but it is a small share of total power, so a kilogram saved is worth about one watt at 20 mph. On a sustained climb it matters far more, because gravity power is directly proportional to total mass. Aero position and tyre choice buy more speed per pound than a lighter frame.
Aerodynamic drag depends on the speed of the air passing you, not your speed over the ground. A 10 mph headwind while riding at 18 mph means your body is fighting 28 mph of air. Because drag scales with the square of that number, the extra power required is far more than the wind speed suggests.