How accurate is this calculator?

It uses the Martin et al. (1998) road-cycling power model — validated to within ~3 W (R²=0.97) — and is accurate to within a few percent in still air. It already includes a ~2.4% drivetrain loss, so the watts you enter are pedal (crank) power. Real-world wind, gusts, road surface variation and changing position are the main remaining sources of error.

What CdA value should I use?

Typical values: hoods position 0.35-0.40, drops 0.30-0.35, aero bars 0.22-0.28. A professional TT rider may achieve 0.20.

Coefficient of rolling resistance. Typical values: racing tyres on smooth road 0.003-0.005, all-round tyres 0.005-0.007, mountain bike tyres 0.010-0.015.

Does this account for wind?

This calculator assumes still-air conditions. Use the Wind Resistance Calculator for headwind/tailwind effects.

BikeCalcs

Power to Speed Calculator — Estimate Speed from Watts

Estimate cycling speed from power output accounting for all resistances.

Power Output

Sustained power at the pedals, e.g. 150–250 W endurance, 250–350 W threshold

Total Weight (rider + bike)

Rider + bike + kit combined, e.g. ~83 kg for a 75 kg rider on an 8 kg bike

CdA (Drag Area)

Hoods ~0.35, Drops ~0.32, TT ~0.24

Crr (Rolling Resistance)

Road tyre ~0.005

Gradient

Road slope %: positive uphill, negative downhill, 0 for flat

How We Calculate This

Speed from Power Formula

This uses the Martin et al. (1998) road-cycling power model. The power that reaches the road equals the sum of three resistance forces multiplied by speed, where θ = arctan(gradient ÷ 100):

Aerodynamic drag: P_aero = 0.5 × air density × CdA × v³
Rolling resistance: P_roll = Crr × mass × g × cos(θ) × v
Gravity: P_grav = mass × g × sin(θ) × v

Not all of your pedal power reaches the road — the chain and bearings lose roughly 2.4%, so road power = 0.976 × rider power. The calculator uses Newton-Raphson iteration to solve for the speed where P_aero + P_roll + P_grav = 0.976 × P_rider.

Frequently Asked Questions

Related Calculators

Watts Per Kilo Calculator

Calculate your power-to-weight ratio in watts per kilogram.

Climbing Power Calculator

Calculate the power needed to climb at a given speed and gradient.

Drag Calculator

Calculate aerodynamic drag force at different speeds.

CdA Calculator

Estimate your drag coefficient area from field test data.

Wind Resistance Calculator

Calculate the effect of headwind and tailwind on power requirements.

Last updated: February 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.