Cycling Wattage Calculator

Estimate the power in watts you need to ride at a given speed, from rolling resistance, aerodynamic drag, and climbing grade.

Quick Facts

Model
P = (rolling + gravity + aero drag) × speed ÷ drivetrain efficiency
Physics-based power model; air density 1.225 kg/m³ (sea level, 15 °C), drivetrain efficiency 97.6%.

Your Results

Calculated
Power required
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At the pedals (watts)
Aerodynamic drag
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Power to overcome air
Rolling resistance
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Power lost to tires
Climbing
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Power against gravity

Ready

Enter your speed, mass, and terrain, then calculate.

About cycling power

The power a cyclist must produce is set by three forces the bike has to overcome: friction between the tires and the road (rolling resistance), the push of the air (aerodynamic drag), and — on any slope — gravity. This calculator adds those three resistive forces, multiplies by your speed to convert force into power, and divides by drivetrain efficiency to account for losses in the chain and bearings. The result is the power you need to sustain that speed on that terrain, expressed in watts.

The formula

Working in SI units (metres, seconds, kilograms), with speed v in m/s and grade expressed as a slope angle θ = arctan(grade%/100):

  • Rolling resistance: Froll = m · g · Crr · cos θ
  • Gravity (climbing): Fgrav = m · g · sin θ
  • Aerodynamic drag: Faero = ½ · ρ · CdA · (v + vwind)²
  • Power at the pedals: P = (Froll + Fgrav + Faero) · v ÷ ηdrivetrain

Here g = 9.807 m/s² (gravitational acceleration), ρ = 1.225 kg/m³ (air density at sea level, 15 °C), CdA is the rider's drag area, Crr is the rolling-resistance coefficient, and η is drivetrain efficiency (this tool uses 0.976, i.e. a 2.4% loss). Note that the aerodynamic force uses air speed — your ground speed plus any headwind — but power is converted using ground speed, because that is the rate at which you cover distance.

Why each term matters

  • Aerodynamic drag grows with the square of air speed, so aero power grows with the cube of speed. Above about 25 km/h on flat ground it is the dominant cost — which is why position, clothing, and wheels matter most at speed.
  • Rolling resistance is roughly constant with speed and scales with weight. Good tires at correct pressure (Crr ≈ 0.004) noticeably beat worn or under-inflated ones (Crr ≈ 0.008 or higher).
  • Climbing depends only on weight and gradient, not speed. On a steep climb it swamps the other two terms, which is why weight — of both rider and bike — matters so much when the road tilts up.

Typical reference points

  • A fit recreational rider sustains about 200–250 W for an hour; a trained amateur racer 280–330 W; elite professionals exceed 400 W at threshold.
  • For an 80 kg system on flat road, no wind, CdA 0.32, Crr 0.005: roughly 105 W holds 26 km/h, ~175 W holds 32 km/h, and ~320 W holds 40 km/h.
  • Power-to-weight ratio (W/kg) predicts climbing performance: ~3 W/kg is solid recreational, ~4 W/kg is competitive amateur, and 6+ W/kg is world-class over an hour.

Frequently Asked Questions

Is this the power at the pedals or at the wheel?
The calculator reports power measured at the pedals (crank), which is what a power meter and your training zones use. It computes the power actually delivered to the road to overcome the three resistances, then divides by drivetrain efficiency (97.6%) to add back the small amount lost in the chain and bearings. If you want power at the rear wheel instead, multiply the result by 0.976.
What CdA and Crr values should I use?
CdA (drag area) depends on position: roughly 0.40 m² sitting upright, 0.32 m² on the hoods of a road bike, 0.28 m² in the drops, and 0.22–0.25 m² in an aero time-trial tuck. Crr (rolling resistance) is about 0.004 for fast tires at high pressure on smooth asphalt, 0.005–0.006 for typical training tires, and 0.008+ on rough or wet roads. The defaults (CdA 0.32, Crr 0.005) suit a road bike on the hoods on decent pavement.
Why does a small speed increase need so much more power?
Because aerodynamic power scales with the cube of speed. Going from 30 to 33 km/h — only 10% faster — raises the aero term by about 33%, and aero is the biggest term at those speeds. That cubic relationship is why the last few km/h of a sprint cost dramatically more watts than the first, and why drafting, which reduces your effective air speed, saves so much energy.
Does this account for wind and hills?
Yes. Enter a positive headwind to add to your effective air speed (a tailwind is a negative value), and enter the road grade as a percentage — positive for a climb, negative for a descent. On a steep descent the gravity term becomes negative, and the calculator will show that gravity is helping rather than costing power. It does not model acceleration, cornering, or changing wind mid-ride; it computes the steady-state power to hold the speed you enter.

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