Cycling Power Output Calculator
Estimate the watts you must produce to ride at a given speed on any gradient. Use it when planning training targets, comparing climbs, or dialing in aerodynamic setups.
About this calculator
Cycling power output is the sum of three resistive forces multiplied by your velocity: gravitational climbing force, rolling resistance, and aerodynamic drag. The formula is: P = v × (9.81 × m × sin(arctan(g/100)) + 9.81 × m × Crr × cos(arctan(g/100)) + 0.5 × 1.225 × CdA × v²), where v is speed in m/s (km/h ÷ 3.6), m is total mass in kg, g is gradient in %, Crr is the coefficient of rolling resistance, and CdA is the aerodynamic drag area in m². At flat zero gradient, the climbing term disappears and drag dominates at high speeds. On steep climbs, gravity becomes the largest force and aerodynamics matter less. Understanding each component helps cyclists prioritize whether to train for power, lose weight, or improve their position.
How to use
Suppose a 75 kg rider on a 9 kg bike (total 84 kg) rides at 30 km/h (8.33 m/s) on a 5% gradient, with CdA = 0.35 and Crr = 0.004. Climbing force: 9.81 × 84 × sin(arctan(0.05)) ≈ 9.81 × 84 × 0.04996 ≈ 41.2 N. Rolling resistance: 9.81 × 84 × 0.004 × cos(arctan(0.05)) ≈ 3.3 N. Drag: 0.5 × 1.225 × 0.35 × 8.33² ≈ 14.9 N. Total force ≈ 59.4 N. Power = 59.4 × 8.33 ≈ 495 W. That is a very hard effort, confirming the significant cost of climbing at speed.
Frequently asked questions
What does CdA mean and how do I find my value for the cycling power calculator?
CdA stands for Coefficient of drag times frontal Area, expressed in m². It is the single most important aerodynamic parameter for a cyclist. A rider in an upright commuter position typically has a CdA around 0.55–0.65 m², a road cyclist in the drops sits around 0.30–0.40 m², and a time-trial position can reach 0.20–0.25 m². You can estimate your CdA from a virtual elevation protocol using a power meter and GPS data, or measure it in a wind tunnel. Using the correct CdA makes the calculator's power estimates much more accurate, especially at speeds above 25 km/h where drag dominates.
How does road gradient affect the power required to cycle at a constant speed?
Gradient has an exponential effect on required power because it adds a gravitational climbing force proportional to sin(arctan(gradient/100)). On flat ground a 75 kg system at 30 km/h might need around 160 W; at 5% gradient that climbs to roughly 490 W — a tripling of effort. Every additional 1% of grade adds approximately 8–10 W per 10 kg of total mass at typical climbing speeds. This is why professional climbers obsess over power-to-weight ratio rather than absolute power.
What is a good rolling resistance coefficient (Crr) for road cycling?
Crr values for bicycle tires typically range from 0.002 for a premium latex-tubed clincher or tubular on smooth asphalt up to 0.008 or higher for a cheap commuter tire on rough pavement. Continental GP5000 and similar high-end tires measure around 0.003–0.004. Tire pressure, tire width, road surface, and temperature all influence Crr. At typical cycling speeds, rolling resistance contributes 10–20 W on flat roads, making it less impactful than aerodynamic drag above 25 km/h but still meaningful over long rides.