Bicycle Gear Inches Calculator

Gear inches only accounts for wheel diameter and the chainring/cog ratio — it ignores crank arm length entirely, even though a longer crank gives you more leverage to turn the same gear. Gain ratio multiplies the same chainring/cog ratio by wheel radius divided by crank length, so two bikes with identical gear inches but different crank lengths will show different gain ratios, which is the number that actually reflects how hard the pedals feel to push.

Gear inches scales directly with wheel diameter — a bigger wheel diameter number produces a proportionally bigger gear inches figure for the same chainring/cog combination. Development follows the same relationship since it's just gear inches multiplied by pi, so both numbers move together; only the gain ratio is less sensitive to wheel diameter changes because it uses wheel radius alongside crank length rather than diameter alone.

Enter your typical or target pedaling cadence in revolutions per minute — most road cyclists ride between roughly 80-100 RPM at cruising effort. The calculator multiplies your development distance (feet traveled per crank revolution) by that cadence and by 60 seconds, then divides by 5,280 feet per mile to get mph, so a higher cadence in the same gear directly produces a higher computed speed.

The speed calculation assumes your entered wheel diameter exactly matches your actual rolled-out tire circumference, but that varies by tire width and inflation even within the same nominal size — 700c tires alone range from about 26.3 to 27+ inches overall. It also doesn't account for drivetrain losses, wheel slip, or terrain, so it's best used as a gearing-comparison tool rather than a precise speedometer.