Bike Gear Calculator

Created by Hanna Pamuła, PhD
Reviewed by Bogna Szyk and Steven Wooding
Last updated: Jan 11, 2023

Our bike gear calculator may help you in choosing chainrings and cogs. Many contemporary bicycles have multiple gears and thus many possible bike gear ratios. Select the range of gear teeth and check which combination best suits your cycling preferences and conditions. As a result, you will get the tables in gear ratio and gear inches units.

What is a gear ratio and gear inches?

Gears are used to increase the force or speed and gear ratio is a unit of bike gearing. To calculate the gear ratio, divide the number of teeth on the front chainring by the number of teeth in a rear sprocket:

gear ratio = (number of teeth in front chainring) / (number of teeth in rear sprocket)

For example, if the number of teeth is even, the gear ratio equals 1. For 50 teeth in front and 25 in the back, the gear ratio is 2.

For bicycles equipped with hub gears, the gear ratio also depends on the internal planetary gears within the hub, so gear ratio is not a good measure when planetary gears are involved.

Gear inches is another relative measure of bicycle gearing. It corresponds to the diameter of the main wheel of an old-fashioned penny-farthing bicycle with equivalent gearing. Gear inches are calculated as the gear ratio multiplied by wheel diameter (in inches) and are usually rounded to the nearest whole number:

gear inches = wheel diameter × (number of teeth in front chainring) / (number of teeth in rear sprocket)

Why don't we use the chainring and rear sprocket teeth values as a measure of a gear? Let's answer with the question: do you know instantly that 39/14 is the same gear as a 53/19? Probably not. That way of showing the ratio is inconvenient and can be confusing. One value explaining that the gear ratio (or gear inches) for both combinations equals 2.79 (or 78) is much easier.

How does the bike gear ratio calculator work?

Our bike gear calculator can show the ratios for the range of chainrings and cogs teeth so that you can check your bike gear ratios and gear inches in different settings:

  1. Choose the minimal value of the teeth in the chainring. Let's say it's 42.

  2. Pick the maximum number, 48, for example.

  3. Analogically, select the range for cogs teeth, for instance, 10 to 24.

  4. If you want to see not only the gear ratio but also the gear inches table, enter the wheel diameter in inches.

  5. Great! The bike gear calculator displayed two nice tables with gear ratios and gear inches for all combinations in chosen range.

Ready for a bike trip? Check our other calculators for cyclists, such as calories burned biking, biking life gain calculator, or the car vs. bike calculator.

Hanna Pamuła, PhD
Chainring (front gears)
Cog (rear gears)
Wheel diameter
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