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BMX Gearing Calculator

Date: 16 August 2012

This gearing chart is here as a guide only. Whilst the calculations it performs are correct, it pays to take into account the following;

  • The 'real' diameter of 20 Inch (or 24 inch) BMX tyres is often slightly more, or less, than the standard 20 or 24 inches.
  • To be totally accurate with your gearing, you need to measure the diameter of the rear tyre you are running on your bike and use that value in this calculator - rather than just the standard 20 or 24.
  • Measure each different rear tyre that you might be running and perform separate calculations for each
  • Many 20 inch tyres are actually between 19.5 and 19.75 inches in diameter.

Chain Ring: (number of teeth)
Free Wheel/Cassette Sprocket: (number of teeth)
Wheel Diameter: (number - inches)
Pedal RPM: (number - rpm)
Calculated Results  
Gear Ratio
Gear-Inches -- (this is what people use as their gearing number)
Actual Rollout -- (distance travelled, in inches, over one full 360 degree pedal revolution)
Speed at Pedal RPM -- kph