Cycling Power (Watts) Calculator
Estimate the watts required to hold a given speed on a given gradient, with a breakdown of where the power goes.
How to use the cycling power calculator
- Enter your total mass (rider + bike + kit).
- Enter your target speed and the gradient.
- Click Calculate to see the power required and its breakdown.
A model, not a measurement
This uses typical road values for drag and rolling resistance. Your real power depends on riding position, road surface, tires and wind, so treat it as a well-informed estimate.
Where your watts actually go
The power you produce is split between overcoming air resistance, climbing against gravity, and fighting rolling resistance and drivetrain losses. On the flat, aerodynamic drag dominates; on a climb, gravity takes over. Understanding the breakdown shows why aero matters at speed and why weight matters uphill.
Estimating the power a speed requires
This calculator estimates the watts needed to hold a given speed on a given gradient for your weight and setup. It is useful for pacing climbs, setting realistic targets, and seeing how much extra power a faster flat speed truly demands, which is often surprisingly large.
Approximate power to hold a speed (83 kg rider + bike, no wind)
| Speed | Flat | 2% climb | 5% climb |
|---|---|---|---|
| 15 km/h | 30 W | 100 W | 205 W |
| 20 km/h | 60 W | 150 W | 290 W |
| 25 km/h | 95 W | 215 W | 390 W |
| 30 km/h | 150 W | 290 W | 500 W |
| 35 km/h | 225 W | 390 W | 635 W |
| 40 km/h | 325 W | 510 W | 790 W |
Modelled for an 83 kg rider-plus-bike in a road position (CdA ≈ 0.32) on good tyres with no wind. Flat-ground watts roughly double from 30 to 40 km/h because aerodynamic drag rises sharply with speed, while on climbs it is weight and gradient that dominate.
Frequently asked questions
How much power to ride 30 km/h?
On flat ground a typical road rider needs roughly 150–200 watts to hold 30 km/h, depending on position, weight and aerodynamics.
What slows a cyclist down most?
On the flat, air resistance dominates and grows with the cube of speed. On climbs, gravity takes over, which is why power-to-weight matters uphill.
Why does a small speed increase need so much more power?
On the flat, most power fights air resistance, which grows with the cube of speed for power. Going a little faster therefore costs disproportionately more watts.
What matters most for climbing power?
Gravity dominates on climbs, so total weight and the gradient set the power required. This is why power-to-weight is the key climbing metric.
How can I go faster for the same power?
Improve aerodynamics (position, clothing, equipment) on the flat and reduce weight for climbs. Both let a given wattage produce more speed.
How many watts does it take to ride at 30 km/h?
On flat ground, an 83 kg rider-plus-bike in a road position needs roughly 150 watts to hold 30 km/h, rising steeply with speed and gradient as the table below shows. Your own figure shifts with weight, position and wind.
Related tools
Power-to-Weight Calculator
Calculate your watts per kilogram (W/kg) — the number that best predicts climbing and racing performance.
FTP Calculator
Estimate your Functional Threshold Power from a 20-minute test and get your full set of power training zones.
Climbing Time Calculator
Estimate your time up a climb from your power and weight, plus your climbing rate (VAM).