Quickly estimate the speed you can hold at a given power, or the power required to hold a target speed, using a typical road setup — on flat or graded terrain.
Assumes a typical road setup (hoods position, standard wheels, race tires, a well-lubricated drivetrain) at sea level. For control over aerodynamics, tires and elevation, use the Cycling Watts Calculator.
On flat ground at moderate-to-high speed, aerodynamic drag is the dominant resistive force, and drag power scales with the cube of speed. That's why racing a few km/h faster costs disproportionately more power than the same speed increase at a gentle pace — and why small aerodynamic gains (position, equipment) matter most for faster riders.
Add even a gentle uphill grade and gravity — not drag — quickly becomes the dominant force, which is why the same power output produces such different speeds on a climb versus flat ground. See the Hill Climb Calculator for a tool built specifically around sustained climbs.
Take a 165 lb rider on an 18 lb bike, riding on the hoods with standard wheels and race tires, on flat ground with no wind, holding a steady 200 W:
Enter 200 W into the calculator above (Watts → Speed) to see this same result, or switch to Speed → Watts to work the calculation in the other direction.
