Gear Inches Calculator

About this calculator

Gear inches is a traditional measurement cyclists use to compare gear ratios across bikes with different wheel sizes and drivetrain setups. It is calculated as the wheel diameter (in inches, including the tire) multiplied by the ratio of chainring teeth to rear cog teeth: wheel diameter × (chainring / cog). The unit dates back to the era of penny-farthing bicycles, where the front wheel's actual diameter determined how far you traveled per pedal stroke — modern gearing recreates that same 'effective wheel size' for comparison purposes.

Cyclists, bike fitters, and mechanics use gear inches to choose appropriate gearing before a ride: lower gear inches (a small chainring paired with a large cog) suit steep climbs where you need to spin easily, while higher gear inches suit flat, fast terrain or sprinting. It is especially useful for comparing gearing across bikes with different wheel sizes — a 700c road bike versus a 26-inch mountain bike — where comparing chainring and cog teeth alone would be misleading.

This calculator also computes development, the actual distance traveled per pedal revolution, giving you both the classic gear-inch number and its real-world rollout distance.