Cadence to Speed Calculator (Cycling)

Cadence to Speed

Cadence is how fast you spin the cranks, in revolutions per minute (RPM). Combined with gearing and wheel size, cadence determines how fast the bike actually moves.

Formula

Speed = cadence × gear ratio × wheel circumference

In SI units:

• speed (m/min) = RPM × (chainring / cog) × π × wheel diameter (m)
• multiply by 0.06 → km/h
• or by 0.0373 → mph

Worked Example: 50/15 at 90 RPM, 700×25c

A 700c rim is ISO 622, and a 25 mm tyre adds 25 mm at the top and 25 at the bottom, so the wheel measures 672 mm across.

• Wheel diameter 672 mm → circumference 2.111 m
• Ratio = 50 / 15 = 3.333
• Speed = 90 × 3.333 × 2.111 = 633 m/min
• = 38.0 km/h = 23.6 mph

Cadence Reference Bands

These are the bands the calculator reports against, so a cadence you type in will be described by whichever row it lands in.

Why Cadence Matters

For the same bike speed, lower cadence with a bigger gear loads the muscles more, which suits short bursts and tires you out over a long ride. Higher cadence with a smaller gear shifts the load to the cardiovascular system, so it is easier on the legs and harder on the lungs. Cyclists typically train to hold 85 to 95 RPM as their natural endurance cadence.

Effect of Wheel and Tire Size

The rim numbers make this look like a bigger deal than it is. A 26" mountain rim is 559 mm and a 700c road rim is 622 mm, an 11% gap, so you would expect the mountain bike to be a lot slower at the same cadence. It is not, because you have to measure the whole wheel including the tyre, and the mountain bike is wearing a much fatter one.

A 26 × 2.1" wheel is 559 + 2 × 53 = 665 mm overall. A 700 × 25c is 622 + 2 × 25 = 672 mm. That is a difference of one per cent, well inside the error of your tyre pressure. Put a 29er wheel on instead (622 + 2 × 53 = 728 mm) and the mountain bike is now the taller of the two.

So gearing, not wheel size, is why a road bike is faster at the same cadence. Measure the rolling diameter of what you actually ride rather than trusting the number stamped on the rim.

Power Connection

Power (watts) = torque × angular velocity. At fixed power, halving the cadence doubles the torque your legs deliver. That is useful for climbing in low gears and hard on the knees over years. This calculator gives the kinematic speed. Aero drag, grade, rolling resistance and your own legs decide whether that speed is available.