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Bicycle Gear Ratio Calculator

Enter chainring, cog and wheel size to find your gearing.

How it is calculated

Three values are derived in sequence. The ratio is R = Tchainring / Tcog, with both tooth counts as plain numbers. Gear inches are GI = R × D, where D is the overall wheel diameter in inches, tyre included. Development, the distance rolled per crank revolution, is M = GI × 0.0254 × π in metres.

The engine keeps the unrounded ratio for the later steps and only rounds each displayed figure to two decimals. The wheel and cog must be greater than zero, otherwise nothing is returned; a chainring of 0 simply gives zeros. The wheel diameter is read in inches, so convert a metric size before entering it.

Worked example

A 46-tooth chainring, a 16-tooth cog and a wheel of about 27 inches. Ratio: 46 / 16 = 2.875, shown as 2.88 : 1. Gear inches: 2.875 × 27 = 77.625, shown as 77.63 in. Development: 77.625 in × 0.0254 = 1.9717 m, and multiplying by π gives 6.19 m of travel for each full turn of the pedals. The three results are 2.88 : 1, 77.63 in and 6.19 m.

Try this example →

Common mistakes

  • Entering the wheel size in millimetres, such as 622 for a 700c rim. The field is in inches, so 622 would give a gear of thousands of inches. Use the overall diameter with the tyre, roughly 27 for a typical 700c wheel.
  • Swapping chainring and cog. The front chainring is the numerator; reversing them gives the inverse ratio, a number below 1 that describes a very easy gear.
  • Using the rim diameter instead of the tyre's outside diameter. The tyre adds to the rolling diameter, which changes the gear inches and the distance per revolution.
  • Comparing development figures between bikes with different tyre pressures or sizes as if they were exact. The result is a theoretical rolling distance.
  • Entering the cassette's total tooth count or the number of gears instead of the teeth on the single cog you are riding in.

About this calculator

A bicycle's gear ratio is simply the number of chainring teeth divided by the number of cog teeth — a 50-tooth chainring paired with a 25-tooth cog gives a 2.0 ratio, meaning the rear wheel turns twice per pedal revolution. Multiplying that ratio by the wheel's diameter gives gear inches (a legacy of the old high-wheel penny-farthing, still used to compare gearing across different wheel sizes), and multiplying by the wheel's circumference gives meters of development — the distance traveled per pedal stroke.

This calculator takes chainring, cog, and wheel size and returns all three measures, letting you compare gearing across bikes with different wheel diameters (700c road wheels vs. 26" or 29" mountain wheels) on equal footing. Cyclists, bike fitters, and track/gearing enthusiasts use it to choose chainring/cassette combinations that suit a course's terrain, pick a single-speed or track cog, or compare setups before a component swap.

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Comments (1)

  • Editorial team

    The metres-per-crank-turn figure is the easiest one to turn into a speed. With the default 50/14 setup it is 7.50 m, so at a steady cadence of 90 rpm you would roll about 675 m a minute, roughly 40 km/h. The tool does not compute speed itself, so multiply by your own cadence. Enter the wheel diameter including the inflated tyre. What cassette and chainring combinations are you comparing?

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