Cycling Power Calculator
Calculate the mechanical power output required to ride a bicycle at any given speed using the peer-reviewed Martin et al. mathematical physics model. Factor in rider and bike weight, hill gradient, road surface friction, headwind, and riding posture to evaluate total Watts, power-to-weight ratio (W/kg), and resistance breakdown.
Steady road cycling ground speed in kilometres per hour (30 km/h = 18.6 mph)
Rider dressed body weight including helmet and shoes
Total mass of bicycle, water bottles, cycling computer, and saddle bag
Road incline percentage (0% flat, 5% moderate climb, 10% steep hill)
Rider posture dictates effective frontal surface area and aerodynamic drag coefficient
Rolling resistance coefficient (Crr) based on surface roughness and tyre pressure
True headwind speed entering straight-on (use negative value for tailwind)
Average continuous pedal power demanded from the cyclist legs
How to Use This Calculator
- Enter your intended steady cycling ground speed in km/h.
- Input rider body weight and total bike/equipment weight in kilograms.
- Set the hill grade percentage (0% for flat courses, 6% for typical alpine ascents).
- Choose your riding posture (hoods, drops, or aerodynamic time-trial bars).
- Review total target power in Watts, W/kg, and aerodynamic vs gravity resistance shares.
Formula & Calculation Methodology
Derived from Martin et al. (1998). Aerodynamic drag is proportional to velocity cubed (P_aero = 0.5 × ρ × CdA × v_air² × v_ground). Gravity power equals total mass × g × sin(arctan(slope)) × v. Rolling resistance equals Crr × mass × g × cos(arctan(slope)) × v.
Worked Example
A 72 kg rider with an 8.5 kg bike riding 30 km/h on flat asphalt on the hoods
Frequently Asked Questions
At what speed does aerodynamic drag become the dominant resistance in cycling?↓
On a flat road, aerodynamic drag accounts for over 50% of total resistance once a cyclist exceeds roughly 18 km/h (11 mph). By 30 km/h (18.6 mph), air drag represents over 80% of required power, and at 40 km/h (25 mph), it accounts for roughly 90%.
What is a good power-to-weight ratio (W/kg) for recreational vs competitive cyclists?↓
For functional threshold power (FTP sustained for 60 minutes): Untrained riders typically produce 1.5–2.0 W/kg, recreational club cyclists 2.5–3.2 W/kg, competitive Category 1/2 racers 4.0–4.8 W/kg, and elite Tour de France contenders exceed 5.5–6.2 W/kg.
How much power does riding in the drops save compared to upright hoods?↓
Switching from upright brake hoods (CdA ≈ 0.32) down into the aerodynamic drops (CdA ≈ 0.28) reduces aerodynamic drag by approximately 12% to 15%, saving about 20 to 25 Watts at 35 km/h.
Why does weight matter so little on flat ground compared to climbs?↓
On flat roads, gravity power is zero; weight only influences rolling resistance (which grows linearly with speed and contributes only 15–20% of total resistance). On steep grades (> 7%), gravity accounts for over 85% of total resistance, making W/kg the single decisive factor.
What are the physical limitations of this cycling power model?↓
This calculation assumes constant sea-level barometric pressure (air density ρ = 1.225 kg/m³) and steady-state velocity. Accelerations, cornering braking losses, and drafting behind other riders alter instantaneous power.
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Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.