Cycling Power & Speed Calculator
Enter your power, bike setup, road grade, wind, and distance to estimate steady cycling speed. You can also switch the calculation around to find the crank watts needed for a target speed.
Predicted cycling speed (km/h)33.35
- Required crank power (W)
- 200
- Estimated ride time
- 1 h 11 min 58 s
- Aerodynamic power (W)
- 155.84
- Rolling-resistance power (W)
- 38.16
- Climbing power (W)
- 0
- Drivetrain loss (W)
- 6
- Power-to-weight ratio (W/kg)
- 2.67
Power breakdown
| Component | Watts |
|---|---|
| Aerodynamic | 155.84 |
| Rolling resistance | 38.16 |
| Climbing | 0 |
| Drivetrain loss | 6 |
Assumes steady speed, steady wind, no drafting, and constant position over the entered distance.
The speed solver finds the ground speed where wheel demand equals rider power after drivetrain losses.
How to use this calculator
- Choose whether to calculate speed from power or power from speed.
- Enter rider weight, bike-and-gear weight, CdA, rolling resistance, drivetrain efficiency, and air density.
- Set the road grade and headwind; use a negative headwind for a tailwind.
- Read the headline result, ride time, and watt-by-watt breakdown.
How the cycling power calculation works
This calculator uses a steady-state road cycling model. At a constant speed, the power delivered to the rear wheel is the sum of aerodynamic drag, tire rolling resistance, and the power needed to climb or descend. Drivetrain efficiency then connects rear-wheel power to crank power.
The model uses these terms:
m = rider weight + bike-and-gear weight
theta = atan(grade ÷ 100)
v = ground speed and u = v + headwind, with both speeds in meters per second.
Pa = 0.5 × rho × CdA × u × |u| × v
Pr = Crr × m × g × cos(theta) × v
Pg = m × g × sin(theta) × v
Pw = Pa + Pr + Pg
When calculating required watts for a target speed, the tool divides positive wheel power by drivetrain efficiency. When calculating speed from entered watts, it numerically searches for the ground speed where entered crank power times drivetrain efficiency equals the wheel-power demand.
What moves the result most
Aerodynamic drag grows quickly because relative air speed is squared and then multiplied by ground speed. That is why a small headwind or a higher CdA can add many watts at road speeds, and why doubling power does not double speed. CdA is usually lower in an aero position than upright on the hoods, but the right value depends on the rider, clothing, bike, and fit.
Grade and total weight dominate on climbs. A heavier rider-and-bike system needs more climbing power at the same gradient and speed. Rolling resistance is smaller on smooth pavement but becomes important with rough surfaces, soft tires, or slow speeds where aerodynamic drag is not yet dominant.
What this calculator leaves out
The result is a clean physics estimate, not a full ride simulation. It assumes constant grade, wind, surface, speed, power, position, and drivetrain efficiency. It does not model acceleration, braking before corners, stop signs, drafting, gusts, wheel rotational inertia, tire pressure changes, or position changes during the ride.
On descents, the climbing term is negative. If total wheel power is negative at the entered speed, the calculator reports that as coasting or braking power rather than inventing negative pedaling watts.
Worked example
For the default case, a 75 kg rider on a 9 kg bike enters 200 W, 0% grade, no wind, CdA 0.32 m², Crr 0.005, 97% drivetrain efficiency, and standard sea-level air density. The rear wheel receives 194 W after drivetrain loss. Solving the power balance gives a speed of about 33.4 km/h.
At that speed over 40 km, the estimated ride time is about 1 h 12 min. The breakdown is roughly 156 W to aerodynamic drag, 38 W to rolling resistance, 0 W to climbing, and 6 W lost in the drivetrain.
Common questions
How many watts do I need to ride at a certain speed?
Choose power from speed, then enter the target speed and conditions. The result is crank power, so it includes drivetrain losses between your pedals and the rear wheel.
Why does cycling speed not increase in direct proportion to power?
Aerodynamic power rises roughly with the cube of speed when there is no wind. That means each extra kilometer per hour costs more watts than the one before it, especially above typical endurance speeds.
What CdA should I use?
A relaxed upright road position may be around 0.40 m² or higher, riding in the drops may be closer to 0.30 m², and a dialed time-trial position can be lower. Treat CdA as an estimate unless you have field-test or wind-tunnel data.
How much does a headwind change cycling power?
A headwind raises relative air speed, which strongly increases aerodynamic watts. A tailwind does the opposite, and a tailwind faster than the bicycle can make the aerodynamic term negative in this signed model.
Why does the calculator differ from my outdoor ride?
Real rides include changing wind, grade, surface, drafting, traffic, accelerations, turns, and shifts in body position. Power meters, CdA estimates, tire Crr, and air density can also differ from the values entered here.