Cycling Power Calculator
Free cycling power calculator estimates the watts needed for your speed, grade and weight using aerodynamic drag, rolling resistance and gravity, with the formula shown.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Cycling Power Calculator Works
This calculator estimates the power (in watts) you must produce at the pedals to sustain a chosen speed, given your weight, the road grade and your aerodynamics. It adds up the three forces a cyclist fights — air resistance, rolling resistance and gravity — and divides by drivetrain efficiency.
The Formula
Total power is the sum of three components, all multiplied by velocity v (in m/s), then divided by drivetrain efficiency (~0.97):
P = (½·ρ·CdA·v³ + Crr·m·g·cosθ·v + m·g·sinθ·v) ÷ η
Where:
- ρ = air density (1.225 kg/m³ at sea level)
- CdA = drag area in m² (aerodynamic drag coefficient × frontal area)
- Crr = coefficient of rolling resistance (~0.005 for good road tires)
- m = total mass of rider + bike (kg)
- g = 9.807 m/s²
- θ = slope angle, where tan θ = grade ÷ 100
- η = drivetrain efficiency
The three terms are aerodynamic power, rolling-resistance power, and climbing (gravity) power.
Worked Example
A rider with 80 kg total mass, CdA = 0.35, Crr = 0.005, riding at 30 km/h on flat ground (θ = 0):
- v = 30 ÷ 3.6 = 8.33 m/s
- Aero = ½ × 1.225 × 0.35 × 8.33³ ≈ 124 W
- Rolling = 0.005 × 80 × 9.807 × 8.33 ≈ 33 W
- Climbing = 0 W (flat)
- Total at wheel = 157 W ÷ 0.97 ≈ 162 W
How the Forces Compare
| Scenario | Aero | Rolling | Climbing | Total |
|---|---|---|---|---|
| 30 km/h flat, 80 kg | 124 W | 33 W | 0 W | ~162 W |
| 40 km/h flat, 80 kg | 294 W | 44 W | 0 W | ~349 W |
| 20 km/h, 6% climb, 75 kg | 37 W | 20 W | 245 W | ~311 W |
Using the Result
- Pacing: knowing the watts for a target speed helps you ride within your FTP on long efforts.
- Equipment choices: lowering CdA matters most at high speed; cutting weight matters most on climbs.
- Tuning inputs: drop air density at altitude, raise Crr on rough roads, and account for headwinds by adding them to your speed in the aero term.
Frequently asked questions
How many watts to ride 30 km/h on flat ground?+
For a typical 80 kg rider plus bike with a CdA of 0.35 and Crr of 0.005 in calm air, it takes about 160 watts to hold 30 km/h (about 18.6 mph) on flat ground. Aerodynamic drag accounts for roughly three-quarters of that power at this speed.
What is CdA in cycling?+
CdA is the product of the drag coefficient (Cd) and frontal area (A), measured in square metres. It captures how aerodynamic your riding position and equipment are. Typical values range from about 0.30 for a tucked road position to 0.40 or higher when sitting upright; a TT setup can drop below 0.25.
Why does aerodynamic drag dominate at speed?+
Aerodynamic power scales with the cube of speed (v³), so doubling your speed requires roughly eight times more power to overcome air resistance. Rolling resistance and gravity scale linearly with speed, so above about 20 km/h on the flat, aero drag becomes the largest single force.
How much extra power does climbing need?+
Climbing adds gravitational power equal to mass × g × grade × speed. On a 6% climb at 20 km/h, a 75 kg rider plus bike needs over 300 watts, versus well under 100 watts on the flat at that speed. This is why weight matters most on steep gradients.
Is this calculator accurate for real rides?+
It is a solid physics estimate using standard sea-level air density (1.225 kg/m³) and 97% drivetrain efficiency. Real-world power varies with wind, temperature, altitude, tire pressure and road surface, so treat the result as a close baseline rather than an exact power-meter reading.