About the Cycling Power Calculator
This cycling power calculator estimates how many watts you need to hold a given speed, using the same physics that power meters measure: air resistance, rolling resistance, gravity on climbs and drivetrain losses. Enter your speed, the road gradient, your weight and the bike’s weight, and choose a riding position and road surface.
It is useful for riders without a power meter who want a reasonable wattage estimate from a ride, for planning pacing on a climb, and for seeing how much an aero position, lighter bike or tailwind really saves. The breakdown shows where your watts go — on flat roads most of the effort fights air, while on steep climbs gravity dominates.
Results are an estimate. Real drag area (CdA) varies with body size, clothing and position, and wind is rarely a steady headwind. For a quick reality check, compare the result with known efforts: a fit amateur can hold around 200–250 W for an hour, while professional road racers typically sustain 350–450 W.
With the default inputs, the power required is 150 W. Change any value above to recalculate instantly.
How to use the cycling power calculator
- 1Choose metric or imperial units and enter your speed.
- 2Enter the gradient — 0% for flat roads, negative for descents.
- 3Enter your weight and the weight of the bike with bottles and bags.
- 4Pick your riding position and the road surface.
- 5Add wind, elevation and temperature if you know them, then read the watts and breakdown.
Formula and method
Power at the pedals is the sum of the forces resisting the bike multiplied by its speed, divided by drivetrain efficiency. Aerodynamic drag grows with the square of air speed (rider speed plus headwind), so doubling speed takes roughly eight times the aero power. Rolling resistance and the gravity term both scale with total mass; on a climb, the gravity term m·g·sin θ·v usually dominates.
Air density ρ comes from the barometric formula for the given elevation and the ideal-gas law at the given temperature (1.204 kg/m³ at sea level and 20 °C). Typical drag areas range from 0.23 m² on a time-trial bike to 0.50 m² sitting upright, and rolling-resistance coefficients from 0.004 for good road tires to 0.02 on dirt. Acceleration and bearing losses are ignored, so this is the power for a steady speed.
- ρ
- Air density (kg/m³)
- CdA
- Drag coefficient × frontal area (m²)
- v, w
- Rider speed and headwind speed (m/s)
- Crr
- Coefficient of rolling resistance
- m
- Rider + bike mass (kg)
- θ
- Road angle (atan of gradient)
Worked examples
30 km/h on the flat, hoods position
At 8.33 m/s with sea-level air (1.204 kg/m³) and CdA 0.32, drag costs ½ × 1.204 × 0.32 × 8.33² × 8.33 = 111.5 W. Rolling resistance for 84 kg at Crr 0.005 adds 34.3 W, and a 2.5% drivetrain loss brings the total to about 150 W.
Climbing a 7% grade at 12 km/h
At 3.33 m/s, lifting 84 kg up a 7% grade takes 84 × 9.807 × sin(4.0°) × 3.33 ≈ 192 W. Air and rolling resistance add only about 21 W, and with drivetrain losses the climb needs roughly 218 W — about 2.9 W/kg for a 75 kg rider.
20 mph into a 10 mph headwind, imperial
Riding at 8.94 m/s into a 4.47 m/s headwind means 13.41 m/s of air speed. With CdA 0.28 the drag power is ½ × 1.204 × 0.28 × 13.41² × 8.94 ≈ 271 W, about 2.25 times the 120 W it would take in still air, for a total of about 316 W.
Frequently asked questions
How many watts does it take to ride 30 km/h?+
On a flat road with no wind, a typical rider on the hoods of a road bike needs around 145–165 W to hold 30 km/h (18.6 mph). In the drops it falls to about 135 W and on aero bars below 120 W; sitting upright it can exceed 210 W.
Why does power rise so steeply with speed?+
Aerodynamic drag force rises with the square of air speed, and power is force times speed, so aero power rises with the cube. Going from 30 to 40 km/h on the flat roughly doubles the power you need.
How accurate is a power estimate without a power meter?+
With good inputs, expect within about 10–15% on steady climbs, where gravity dominates and is easy to model. On flat roads the error is larger because drag area and real wind are hard to know.
What is a good watts per kilogram?+
Untrained riders can typically sustain 2–2.5 W/kg for an hour, trained amateurs 3–4 W/kg and professional climbers more than 5.5 W/kg. W/kg matters most on climbs, while absolute watts matter more on the flat.
Does a lighter bike make me much faster?+
Only on climbs. Saving 1 kg on an 84 kg rider-plus-bike system cuts climbing power by about 1.2%, worth a few seconds on a 20-minute climb. On flat roads, aerodynamics matter far more than weight.