Cycling Hill Climb Power Calculator
Estimate the watts needed to ride up any hill.
Enter weight, bike weight, grade, and speed to see power split by gravity, rolling, and aero drag.
The Three Power Components
Cycling power on a climb comes from three sources: lifting your mass against gravity, overcoming rolling resistance, and pushing through aerodynamic drag.
Gravity (the Dominant Term)
P_gravity = total_mass_kg x 9.81 x speed_m/s x sin(arctan(grade/100))
On any climb above 3%, gravity accounts for 80 to 90% of total power. At 5% grade and 10 km/h, a 75 kg rider on a 9 kg bike needs about 156 watts just to fight gravity.
Rolling Resistance
P_rolling = total_mass x 9.81 x Crr x speed_m/s
Crr is the rolling resistance coefficient: roughly 0.004 for supple road tires on smooth pavement, up to 0.012 for off-road conditions. This calculator uses 0.005 as a road tire default.
Aerodynamic Drag
P_aero = 0.5 x air_density x CdA x speed_m/s cubed
CdA (drag coefficient times frontal area) for a road cyclist in a normal riding position is roughly 0.32 m2. At climbing speeds below 15 km/h, aero drag is typically under 10% of total power. At faster climbing speeds on a descent or false flat, it becomes significant.
Effort Zones
Power divided by body weight gives watts per kilogram. Under 2.5 W/kg is easy endurance. 2.5 to 3.5 W/kg is steady endurance. 3.5 to 4.5 W/kg is tempo to threshold. Above 4.5 W/kg is threshold to VO2 max territory. Elite climbers sustain 6+ W/kg on race climbs.
Using the Results
This is a useful tool for pacing unfamiliar climbs. Enter the grade and your target speed to see whether the required power is within your sustainable range. Adjust speed down until the required power matches what you can actually hold.