Cycling Speed to Power Calculator
No power meter? Get a rough sense of the watts behind a given speed from your weight, your bike, and the gradient you're riding.
This is a simplified model that assumes typical road-bike aerodynamics (riding on the hoods), smooth tarmac, and no wind. Real power depends heavily on your position, tires, surface, and the breeze — so treat this as a ballpark for a flat or steady climb, not a substitute for a power meter.
How it works
Power has to overcome three things: air resistance, rolling resistance, and gravity when you climb. This adds those up at your speed and divides by drivetrain efficiency to estimate the watts you'd need.
Aero drag dominates on the flat and grows with the cube of speed, which is why small speed gains cost so much power. On a climb, your weight and the gradient take over as the big factors.
It's deliberately simplified — it assumes typical road-bike aerodynamics on the hoods, smooth tarmac, and no wind. Change your position or add a headwind and the real number moves.
Frequently asked questions
Why does going faster cost so much extra power?
Air resistance rises with the cube of speed, so nudging from 30 to 35 km/h on the flat takes far more than a 17% power bump. That's why aerodynamics — position, clothing, wheels — matters so much to fast riders.
Can I use this instead of a power meter?
Treat it as a ballpark, not a replacement. A power meter reads your actual output through wind, road surface, and position changes that this model can't see. It's great for a rough idea, less so for structured training targets.
What's power-to-weight and why does it matter?
It's your watts divided by your body weight, in W/kg — the number that best predicts climbing. Two riders at the same watts climb very differently if one is lighter, which is why the tool shows it alongside raw power.