Enter your chainring and cog, your usual cadence and your wheel and tire size. The calculator shows how fast that gear moves you, how far one pedal turn takes you and the wheel circumference to enter in a bike computer.

How This Calculator Works

  • Gear ratio = chainring teeth / cog teeth.
  • Development, or distance per pedal turn, = gear ratio x wheel circumference.
  • Speed = development x cadence x 60, converted from meters per hour to miles or kilometers per hour.
  • Gear inches = gear ratio x wheel diameter in inches, a traditional way to compare gears across wheel sizes.

Wheel circumferences come from the standard ETRTO tire size charts that bike computer makers publish. Your real number can be a few millimeters off depending on the tire model and pressure.

Getting a More Accurate Wheel Number

For the best speed and distance readings, measure your own wheel. Put a chalk mark on the tire and a matching mark on the floor, roll the bike forward one full turn with your weight on it, mark the floor again and measure between the two marks in millimeters. Enter that number in your bike computer instead of the chart value.

Limitations

The result is the speed the gear would give you on paper. It says nothing about whether you can hold that cadence in that gear on a climb or into a headwind. It also ignores coasting and assumes no drivetrain slip, which is fine for a derailleur or single speed drivetrain.

Frequently Asked Questions

What cadence should I enter?

Many riders settle around 80 to 95 rpm on flat roads. Casual riders often pedal slower, around 60 to 75 rpm. If you use a cadence sensor, enter your usual average.

Can I use this for a single speed or fixed gear?

Yes. Enter your one chainring and one cog. Gear inches is the number most single speed riders use to compare setups.

Why does my bike computer show a different speed?

Usually the wheel circumference in the computer settings does not match your real tire. Measure a roll out as described above and enter that value.

Does this work for internal gear hubs?

Only partly. Hub gears change the ratio inside the hub, so you would need to multiply the result by the published hub ratio for each gear.