Cycling Power (Wattage) Calculator

The Ultimate Metric of Cycling

In modern cycling, speed and heart rate are considered flawed, secondary metrics. Speed is manipulated by wind; heart rate is manipulated by heat and caffeine.

The absolute truth of a cyclist's fitness is Power, measured in Watts (W). Power is an instantaneous, objective measurement of exactly how much mechanical force your legs are driving into the pedals.

The Physics of the Bicycle

When a cyclist pushes the pedals, that wattage is distributed into overcoming three massive physical forces. If you know these forces, you can mathematically calculate the exact wattage required to maintain a specific speed.

1. Gravity: The force attempting to pull the combined mass of the rider and bike back down the hill.
2. Rolling Resistance ($C_{rr}$): The friction of the rubber tires deforming against the asphalt.
3. Aerodynamic Drag ($C_dA$): The force required to punch a hole through the wall of air in front of the rider.

The Formula

To find the required power, we sum the forces and multiply by velocity:

The Aerodynamic Wall

At 10 mph on a flat road, gravity is zero and air resistance is minimal; you might only need 50 Watts to maintain speed. However, aerodynamic drag increases with the cube of velocity. To ride at 25 mph, you might need 300 Watts—with over 80% of your energy going entirely toward fighting the wind.