Estimate the pedal power needed to ride at a chosen speed from rider and bike mass, gradient, CdA, rolling resistance, wind and drivetrain efficiency.
kg
kg
km/h
%
m²
kg/m³
km/h
%
Results
Calculated
Power at the pedals
—
W, after drivetrain loss
Power-to-weight
—
W/kg of rider mass
Aerodynamic drag
—
W, grows with speed cubed
Rolling resistance
—
W, tires on the road
Climbing (gravity)
—
W, negative on descents
Drivetrain loss
—
W lost in chain and gears
Ready
Enter rider and bike mass, speed and gradient, then press Calculate.
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What this calculator finds
This calculator estimates the power a cyclist must produce to ride at a given speed. It adds up the three forces that resist you (air drag, rolling resistance and gravity on a climb), multiplies by speed to get watts, and then divides by drivetrain efficiency to get the power at the pedals. It also shows watts per kilogram, which is the number that predicts climbing speed.
It is useful for planning a pacing strategy, comparing aero and weight changes, or sanity-checking a power-meter reading.
The equations
Paero = ½ ρ CdA · vair2 · v, where vair is ground speed plus headwind.
Proll = Crr · m g cosθ · v, with m the combined rider and bike mass.
Pgrav = m g sinθ · v, where θ = arctan(gradient / 100).
Ppedal = (Paero + Proll + Pgrav) / efficiency.
Worked example
A 75 kg rider on a 9 kg bike rides at 25 km/h up a 1% grade with CdA 0.32 m², Crr 0.005, air density 1.225 kg/m³, no wind and 97% efficiency, the defaults. Speed is 25 / 3.6 = 6.944 m/s and total mass is 84 kg.
Aero power = 0.5 × 1.225 × 0.32 × 6.9443 = 65.6 W. Rolling power = 0.005 × 84 × 9.807 × 6.944 = 28.6 W. Gravity power = 84 × 9.807 × 0.01 × 6.944 = 57.2 W. The wheel power is 151.5 W, and dividing by 0.97 gives 156.2 W at the pedals, which the calculator rounds to 156 W. That is 156 / 75 = 2.08 W/kg, an endurance effort.
Common mistakes and how to read the result
Using speed in mph. The speed field is km/h.
Ignoring wind. A modest headwind can add more power than a small hill.
Underestimating CdA. A too-low CdA makes the required power look easier than it is.
Expecting a match to every ride. Drafting, surface changes and acceleration are not modelled.
Frequently Asked Questions
What CdA should I use?
About 0.40 m squared for an upright position, 0.32 on the hoods or drops, and 0.25 in an aero tuck or time-trial position. If you do not know yours, 0.32 is a reasonable road-bike value.
Why does the wind field use km/h?
Headwind adds to your ground speed to give the air speed that drives drag. A 10 km/h headwind at 25 km/h means you ride through the air at 35 km/h, which raises the aero power a lot because it scales with the cube of speed.
Why is the aerodynamic term so large at speed?
Drag power grows with the cube of speed, so doubling speed needs about eight times the aero power. Rolling and climbing power grow only in proportion to speed.
How accurate is the result?
Typically within 5 to 10% if CdA and Crr are realistic. The largest errors come from CdA, which varies with position and clothing, and from wind, which changes constantly outdoors.
Practical Guide for Cycling Power Calculator - Calculate Watts for Cycling
Cycling Power Calculator - Calculate Watts for Cycling is most useful when the inputs reflect the situation you are actually planning around, not a best-case estimate. Treat the result as a decision aid: it gives you a structured way to compare assumptions, spot outliers, and decide what to verify next. For Sports work, the most important review lens is repeatability, fatigue, recovery, pacing, training load, and conditions on the day.
Start with a baseline run using values you can defend. Then change one assumption at a time and watch which output moves the most. If one input dominates the result, spend your verification time there first. If several inputs have similar influence, use a conservative scenario and an optimistic scenario to create a practical range instead of relying on a single exact number.
Before acting on the result, compare the result with recent sessions, race logs, and coach feedback instead of relying on a single best effort. This is especially important when the calculator supports a purchase, project plan, performance target, or operational decision. The calculator can make the math consistent, but the quality of the conclusion still depends on current data, clear units, and assumptions that match your real constraints.
When the output looks surprising, slow down and inspect each input in order. A small change in one high-leverage field can move the final number more than several low-leverage fields combined. For Cycling Power Calculator - Calculate Watts for Cycling, that means you should first confirm the value with the greatest scale, then confirm the value with the greatest uncertainty, then rerun the calculator with conservative and optimistic assumptions. This sequence turns the calculator from a single answer into a practical decision range.
Review Checklist
Confirm every input uses the unit and time period requested by the calculator.
Run a low, expected, and high scenario so the answer has a useful range.
Check whether rounding or a missing decimal place changes the decision.
Update the calculation each training block, after a tune-up event, or when volume and intensity change.