Speed to power calculator
This cycling speed to power calculator estimates the power needed to hold a given speed, using rider and bike weight, road grade, riding position and drafting. Set your speed, weights and grade, pick a position from hoods to aero bars, and see power split into its gravity, rolling resistance and aerodynamic parts, plus a table across a range of speeds.
Power
180W
Power by speed
| Speed (km/h) | Power (W) |
|---|---|
| 20 | 66 |
| 25 | 113 |
| 30 | 180 |
| 35 | 271 |
| 40 | 391 |
| 45 | 544 |
How it works
The model sums three physical forces the drivetrain must overcome: gravity on any grade, rolling resistance from tyres on the road, and aerodynamic drag from air pushing back on the rider and bike, then divides by a fixed 97% drivetrain efficiency to account for the roughly 3% lost in the chain and derailleurs (Martin et al., 1998, a widely used cycling power model). That drivetrain loss shows as its own row below the headline power figure.
Aerodynamic drag grows with the cube of speed, so it dominates at higher speeds and on flat ground, while gravity dominates on steep climbs even at modest speed. Riding position sets the frontal area and drag coefficient, CdA, with aero bars cutting drag noticeably below hoods.
Drafting in a group or right behind a wheel cuts the air a rider has to push through, modelled here as a percentage reduction in aerodynamic drag, which is why pack riding costs meaningfully less power than riding solo at the same speed.
Frequently asked questions
How much power do I need to ride 30 km/h?
On flat ground in a normal hoods position, roughly 200 to 230 W for a typical rider and bike weight, mostly spent overcoming air resistance. Any headwind, climb or aero position change shifts that number quickly, which this calculator lets you check directly.
Why does drafting save so much power?
Aerodynamic drag is usually the largest force at road speeds, and drafting directly cuts the air resistance a rider faces by sitting in another rider's wind shadow. Riding on a wheel typically saves noticeably more power than sitting mid-group, which is why breakaways favour cooperation.
Does bike weight matter as much as rider weight?
Only on climbs, where gravity depends on total mass, rider plus bike, moved uphill. On flat ground at speed, aerodynamic drag dominates instead and a few extra kilograms of bike barely change the power required to hold a given speed, which is why light race bikes matter far more in the mountains than on a flat time trial.
Related tools
- FTP zones calculatorCalculate your cycling FTP from a known value or a 20-minute power, free, with the seven Coggan training zones in watts.
- Watts per kg calculatorWork out your cycling power-to-weight ratio and rider category for free, using the Coggan power profile for men and women.
- Climb time calculatorPredict climb time, speed and VAM from length, elevation gain and power, free, with a table across a range of power outputs.
- Bike gear calculatorList every chainring and cassette combination sorted by development, free, with ratio, gear inches and speed at your cadence.
Overload builds your real power curve
Overload records power on every ride and builds your power curve from your actual efforts, not a model. Free on iOS and Android.