Bike Power to Speed Calculator

How fast does 200 watts make you go? It depends. On a flat road in the drops, around 34 km/h. Drop into a 5% climb and the same watts crawl. This calculator runs the cycling power equation in both directions, so you can turn a power number into a speed, or a target speed into the watts it costs.

What the calculator solves

Cycling speed is a balance of three forces fighting your wheels: rolling resistance from the tyres, gravity on a slope, and air drag. Air drag wins above about 25 km/h, which is why aero position matters so much on the flat and so little going uphill.

The tool sums those three forces and the power needed to overcome them. Pick a direction, enter your total weight, the grade, and the wind, then choose an aero position and surface. In power-to-speed mode it solves for the speed your watts can hold. In speed-to-power mode it tells you the watts a target speed demands.

The inputs that move the number

Total weight is rider plus bike plus kit, since gravity does not care which part is which. On a climb this is the input that dominates. On the flat, your aero position carries far more weight than your body does.

CdA is the drag area of you and the bike. Hoods sit around 0.40, the drops near 0.32, a committed aero position near 0.27. Going from hoods to drops at 200 watts on the flat buys you roughly 2 km/h for free. Rolling resistance covers the surface: 0.005 for a good road tyre, 0.008 for gravel. Headwind adds straight onto your speed inside the drag term, so 5 m/s into your face hits harder than the same speed of ground covered.

Reading the result

Use power-to-speed to set a pace you can hold, then check the time and energy for a known distance. The kilojoule figure is close to the kilocalories you burn on the bike, a handy fuelling check for ride calories.

These are steady-state estimates with no drafting. A real ride has surges, corners and gusts, so treat the output as a clean baseline rather than a stopwatch. To compare efforts where the pace was anything but steady, smooth the file with normalized power.

Once you have a speed and the watts behind it, two numbers frame the rest of your engine. Divide power by weight with the power to weight calculator to see your climbing ceiling, and check whether your gearing lets you spin that power on the steep stuff. For a long climb, feed your time and elevation into VAM to track how fast you go up.