Cycling Power Calculator (Watts)
Calculate the watts required to ride at a given speed and grade for your weight, using the standard road-cycling power model — with a breakdown of rolling, gravity, and air resistance. Runs in your browser.
Advanced (rolling resistance, drag area)
Defaults: Crr 0.005 (road tire on asphalt), CdA 0.32 m² (hoods), drivetrain loss 2%, sea-level air. No wind assumed.
Power required
- Required power
- 149 W
- Power-to-weight
- 1.86 W/kg
- — rolling resistance
- 33 W
- — gravity (climbing)
- 0 W
- — air drag
- 116 W
Based on the Martin et al. (1998) road-cycling power model. Real-world power also depends on wind, position, and surface; treat as an estimate.
About this tool
The power a cyclist must produce is the sum of three resisting forces multiplied by speed: rolling resistance between tire and road, gravity when climbing, and aerodynamic drag against the air. This calculator uses the well-established road-cycling power model (Martin et al., 1998) to compute the watts required for a given speed, grade, and total weight, and breaks the result into those three components so you can see what is actually slowing you down. On the flat at moderate speed, air drag dominates and grows with the cube of speed — which is why going faster gets disproportionately harder; on a climb, gravity takes over and scales with your weight and the grade. Sensible defaults are used for rolling resistance, drag area, drivetrain loss, and sea-level air density, all adjustable in the advanced panel, and no wind is assumed. It is a physics estimate for training and planning, not a substitute for a power meter. Everything runs in your browser.
How to use it
- Enter your target speed and the road grade (0 for flat).
- Enter total weight — rider plus bike and kit.
- Optionally adjust rolling resistance (Crr) and drag area (CdA) in the advanced panel.
- Read the required power, your watts-per-kilogram, and the force breakdown.
Frequently asked questions
- What formula does this use?
- The standard road-cycling power equation: power = (rolling + gravity + aerodynamic forces) × speed ÷ (1 − drivetrain loss). Rolling = Crr·m·g·cos(θ), gravity = m·g·sin(θ), and air = ½·ρ·CdA·v². It is the model validated by Martin and colleagues in 1998.
- Why does a little more speed need so much more power?
- Aerodynamic drag rises with the square of speed, and since power is force times speed, the air component grows roughly with the cube of speed. Going from 30 to 40 km/h on the flat can nearly double the power required.
- What is a good watts-per-kilogram figure?
- W/kg is the key climbing metric. Rough sustained (FTP) ranges: recreational riders around 2–3 W/kg, strong amateurs 3.5–4.5, and elite/pro riders 5–6+. This tool shows the instantaneous W/kg for the effort you entered, not your FTP.
- What are Crr and CdA?
- Crr is the coefficient of rolling resistance (about 0.004–0.008 for road tires on asphalt). CdA is your drag area in square meters — frontal area times drag coefficient — roughly 0.3 on the hoods and lower in an aero tuck. Both are adjustable in the advanced panel.
- Does it account for wind?
- No — it assumes still air, so air speed equals ground speed. A headwind effectively raises the air speed (and required power) while a tailwind lowers it. For windy conditions, adjust the speed input to approximate the relative air speed.
- Is this a substitute for a power meter?
- No. It estimates the power needed under idealized assumptions. A power meter measures your actual output including real-world wind, surface, and position effects. Use this for planning and what-if analysis.