Estimate the power in watts you need to ride at a given speed, or how fast you will go with a given power. It models gravity, rolling resistance and aerodynamic drag from your weight, gradient, position, tires, wind, altitude and temperature.
Last updated:
What do you want to calculate?
Units
km/h or mph (per Units)
W
%
Negative for downhill
kg or lb
kg or lb (bike, bottles, shoes, helmet)
m²
km/h or mph
m or ft (thinner air = less drag)
°C or °F
%
Enter your values to see the result.
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How to use the Cycling Power Calculator
Choose a mode: watts for a speed, or speed from watts.
Enter rider and bike weight and the road gradient (negative for downhill).
Pick your riding position and tires, or enter your own CdA and Crr.
Add wind, altitude and temperature if you want more realism.
Read the result and the breakdown of where your watts go, plus the table at other speeds.
The cycling power equation
Force
Formula
What changes it
Gravity
m · g · sin(atan(grade))
Total weight and slope
Rolling resistance
m · g · cos(atan(grade)) · Crr
Tires, pressure, road surface
Aerodynamic drag
½ · ρ · CdA · (v + headwind)²
Position, clothing, wind, air density
Rider power
(sum of forces × v) ÷ (1 − drivetrain loss)
Chain condition and gearing (2–5% loss)
Air density ρ is calculated from altitude (standard atmosphere pressure) and temperature with the ideal gas law; it is about 1.204 kg/m³ at sea level and 20 °C, and roughly 10% lower at 1,000 m. Speed in the formulas is in meters per second.
Typical CdA and Crr values
Position
CdA (m²)
Tire / surface
Crr
Upright city or mountain bike
0.45–0.60
Track tubulars, wooden track
0.002–0.003
Road bike, hands on tops
0.38–0.42
Fast road tires, smooth asphalt
0.003–0.005
Road bike, on the hoods
0.30–0.34
Rough asphalt or chip seal
0.006–0.008
Road bike, in the drops
0.27–0.30
Gravel road
0.008–0.012
Triathlon / aero bars
0.22–0.26
MTB tires on dirt trail
0.012–0.025
Tips
Above about 25 km/h (15 mph) on the flat, aerodynamic drag is the biggest resistance; a lower position saves more watts than a lighter bike.
Drag rises with the square of air speed, so a 15 km/h headwind costs far more than a 15 km/h tailwind gives back.
To estimate your own CdA, ride a steady flat loop at a known power, then adjust CdA here until the speed matches.
Frequently asked questions
How is cycling power calculated?
Power = (gravity force + rolling resistance + aerodynamic drag) × speed ÷ drivetrain efficiency. Gravity = m·g·sin θ, rolling = m·g·cos θ·Crr, and drag = ½·ρ·CdA·(v + wind)². Multiplying each force by speed in m/s gives watts.
How many watts does it take to ride 30 km/h?
On flat ground with no wind, a 75 kg rider on a 9 kg road bike on the hoods (CdA about 0.32 m², Crr 0.004) needs about 145 W at sea level and 20 °C. On aero bars it drops to around 115 W, while sitting upright it rises to about 190 W.
What is CdA?
CdA is the drag coefficient multiplied by frontal area, in square meters. It describes how aerodynamic you and your bike are. Typical values range from about 0.20 m² for a pro time-trial position to 0.45 m² or more sitting upright.
What is Crr?
Crr is the coefficient of rolling resistance of your tires on the surface. Fast road tires on smooth asphalt are around 0.003 to 0.005, gravel around 0.008 to 0.012, and knobby mountain bike tires on dirt can be 0.015 or more.
Why does weight matter more on climbs?
On steep climbs you are slow, so aerodynamic drag is small and most of your power lifts your mass against gravity. Power needed scales almost directly with total weight, which is why watts per kilogram is the key climbing number.
How accurate is this power estimate?
It is a physics model, so accuracy depends on your inputs. Real CdA and Crr vary with clothing, road surface and tire pressure, and wind is rarely steady. Expect results within about 10% of a power meter on steady efforts if your inputs are realistic.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.