Calculate bicycle horsepower and watts from road speed, rider and bike weight, grade, riding position, wind, hill-climb data, or measured cycling power.
Formula
Riding Power mode (sum of rolling, gravity, and aerodynamic power):
P = Crr·m·g·cos(θ)·v + m·g·sin(θ)·v + ½·ρ·CdA·v³
HP = P ÷ 745.7
where P = power in watts, Crr = 0.005 (rolling resistance), m = rider + bike mass (kg), g = 9.81 m/s², θ = atan(grade%/100), v = speed (m/s), ρ = 1.225 kg/m³ (air density), CdA = drag area set by riding position.
Hill Climb mode (gravity-only estimate):
P = m·g·h ÷ t
HP = P ÷ 745.7
where m = rider + bike mass (kg), h = elevation gained (m), t = climb time (s).
Interpretation
The result is the mechanical power you deliver to move the bike, expressed in horsepower, watts, metric HP, and food calories per second. A trained cyclist produces far less horsepower than a small engine — sustained output above 0.3 HP is already a hard effort. Use these watt bands as a reference for sustained (roughly 20–60 minute) power:
- Under 75 W (≈0.10 HP): very light, casual cruising.
- 75–150 W (≈0.10–0.20 HP): recreational / commuting pace.
- 150–230 W (≈0.20–0.31 HP): fit recreational cyclist.
- 230–320 W (≈0.31–0.43 HP): strong amateur, hard tempo.
- 320–420 W (≈0.43–0.56 HP): racer near threshold.
- 420–650 W (≈0.56–0.87 HP): elite / short hard efforts.
- 650 W+ (0.87+ HP): sprint peaks, sustainable for only seconds.
How Each Force Affects Your Power
| Force | Dominates When | Scales With |
|---|---|---|
| Aerodynamic drag | Flat ground, speed above ~15 mph | v³ (cubed) |
| Gravity (climbing) | Grade above ~3% | Weight × grade × speed |
| Rolling resistance | Low speed, soft tires | Weight × speed |
FAQ
What weight should I enter — just me, or me plus the bike?
Enter combined rider plus bike (plus bottles and any gear). A road bike adds roughly 15–20 lb and a typical hybrid or mountain bike 25–35 lb.
Why does the Hill Climb mode give a lower number than Riding Power on the same hill?
Hill Climb mode counts only the work done against gravity. On real climbs, rolling resistance and air drag add another 10–20% at typical speeds, so the Riding Power estimate is closer to total effort.
How do I choose a riding position?
Pick the option that matches your body shape during the effort: sitting upright on a commuter, hands on the brake hoods, down in the drops, or tucked on aero bars. Each option changes the drag area (CdA), which has a large effect at higher speeds because drag scales with v³.
Is horsepower the same as watts on a power meter?
Yes, just different units. 1 HP ≈ 745.7 watts, so a 250 W rider is producing about 0.335 HP. This calculator estimates that same mechanical power from speed or climb data when you don’t have a meter.
