Cycling Power Calculator

Aerodynamic drag scales with the cube of your relative airspeed, while rolling resistance and climbing power scale only linearly with weight. At typical road speeds drag is the largest of the three components, so a modest change in speed swings total power well beyond what the same percentage change in rider-plus-bike weight would produce.

Enter a positive number for a headwind, which adds to your ground speed to raise the relative airspeed your body pushes through and increases air resistance power. Enter a negative number for a tailwind, which lowers that relative airspeed -- and if the tailwind is stronger than your ground speed, the air resistance term actually turns negative, meaning the wind is pushing you rather than slowing you down.

Climbing power depends on the vertical component of your motion, which is proportional to the sine of your grade angle. At a 0% grade there's no vertical rise or fall, so that term is zero and no power is spent -- or gained -- fighting gravity, regardless of your weight or speed.

A negative grade (downhill) makes climbing power negative, meaning gravity contributes power rather than you, which reduces the power you personally need to supply compared to flat ground at the same speed. If that downhill assist exceeds your rolling resistance and air resistance combined, the model's Total Power figure can go negative, meaning gravity alone would carry you at least as fast as your target speed without any pedaling.

It doesn't model drivetrain efficiency losses, changes in tire pressure or road surface, rider position and aerodynamic equipment like aero bars, drafting behind another rider, altitude-driven air density changes, or acceleration -- it assumes you're already holding a constant speed, not the extra power needed to get up to it.