Cycling Power Estimates: What Speed Costs in Watts
Power rises steeply with speed, which is why small speed gains cost so much effort. This post walks through the simple model behind the estimate.
What is the Cycling Power Estimator?
This estimator combines a simple air-resistance term with a rolling term to give a ballpark wattage for flat, calm conditions. Enter your speed and combined rider-plus-bike weight and the tool returns the estimate. It is an estimate only: wind, gradient, position, and tyres can move the real figure a long way.
How to use it
- Enter your steady speed in kilometres per hour.
- Enter rider plus bike weight in kilograms.
- Click Estimate Power.
Worked example
At 30 km/h with 85 kg of rider and bike, the estimate is about 237.96 watts.
Why does 30 km/h cost far more than 20 km/h?
Air resistance grows with the cube of speed, so each extra kilometre per hour costs more watts than the last one did.
Frequently asked questions
Does weight matter much on the flat?
Less than at climbing speed. On the flat, air resistance dominates and weight plays a smaller role.
Is this a substitute for a power meter?
No, it is a planning estimate. A power meter measures what you actually produce.