CalculatorsSpeed to Watts Calculator
Speed to Watts Calculator
On the flat, most of your watts fight air. CdA is the drag area: about 0.30–0.35 for many riders on the hoods, lower in the drops, higher sitting upright.
Inputs
Results
- Power
- 227 W
How the number is made
Power = ½ × CdA × 1.225 × v³ + Crr × mass × g × v + mass × g × v × gradient. Speed is converted from km/h to m/s. Air density is fixed at 1.225 kg/m³ (sea level, about 15°C).
Mass is rider plus bike. No wind, no drafting, and no extra drivetrain loss. Air density stays 1.225 kg/m³, so altitude and heat are not applied. A tailwind makes this number optimistic if you enter ground speed. A result below zero is shown as 0.
Related calculators
- Power-to-Weight Calculator
Use these watts with body weight when the road turns uphill.
- Cadence to Speed Calculator
The speed you just entered has to be a gear you can actually turn.
Questions
What CdA should I enter?
0.32 is a reasonable hoods start. Time-trial positions can approach 0.20. An upright city bike can exceed 0.40.
Why does a descent show few watts?
Gravity is helping. The calculator floors the result at zero — it will not show a motor braking you.
Which mass belongs in the speed-to-watts tool?
System weight: rider plus bike. Air density stays at 1.225, about sea level at 15 degrees C. A result below zero is shown as zero.
Related gear
- Aero helmet
CdA moves more watts than a lighter bottle cage once you are above 30 km/h.
$150–$350