Cycling Power Calculator
Estimate the power output in watts needed to maintain a cycling speed from rider and bike weight, road gradient, and headwind.
kg
kg
km/h
%
Use a negative number for a downhill grade.
km/h
Use a negative number for a tailwind.
Estimated Power Required
149 W
Rolling Resistance
32 W
Aerodynamic Drag
113 W
Gradient (Gravity)
0 W
How Cycling Power Output Is Estimated
Sustaining a given speed on a bike takes power to overcome three physical forces: rolling resistance between the tires and the road, aerodynamic drag from the air, and — on a climb or descent — gravity. This calculator adds up all three using standard cycling physics formulas and typical default coefficients (a rolling resistance coefficient of 0.005 and an effective frontal area, CdA, of 0.32 m²), then adjusts for a small drivetrain efficiency loss.
Example
A 70 kg rider on a 9 kg bike (79 kg total) riding at 30 km/h on flat ground with no wind needs roughly 200-220 watts, mostly to overcome aerodynamic drag, which grows with the cube of speed. Add a 3% climb at the same speed and the required power roughly doubles, since gravity now takes a large share of the total.
Common Use Cases
- Estimating the power needed to hold a target speed on a route with a known gradient.
- Comparing how much a headwind or a climb increases the power required versus flat, calm conditions.
- Sanity-checking a power meter reading against a physics-based estimate.
FAQs
Why might my actual power meter reading differ from this estimate?
Real-world power depends heavily on things this simplified model doesn't measure directly — your riding position, bike and wheel aerodynamics, tire pressure and road surface, drivetrain condition, and variable wind. This calculator uses reasonable average defaults, so treat the result as a solid ballpark rather than an exact figure.
Why does aerodynamic drag matter so much at higher speeds?
Aerodynamic drag power scales with the cube of your speed (roughly), so doubling your speed on flat ground can increase the drag component by roughly eightfold — which is why drag dominates the power requirement at typical road cycling speeds above about 25-30 km/h.
Can this handle a downhill (negative) gradient?
Yes — enter a negative number for the gradient. On a steep enough descent, the gravity term can turn negative and offset rolling resistance and drag entirely, which is why coasting downhill often requires no pedaling power at all.