Gear Inches Calculator

Gear inches is a wonderfully old-fashioned but still useful way to compare how hard or easy a bicycle gear is to push. It dates back to the penny-farthing era, when a bike's “gear” literally was the diameter of its big front wheel. This gear inches calculator converts any chainring-and-cog combination into that single comparable number — and into development, the distance you travel per pedal stroke.

The Formula

Gear inches is the effective diameter of the driven wheel as if it were a direct-drive penny-farthing:

A bigger chainring or a smaller cog raises the gear (harder, more speed per stroke). A smaller chainring or larger cog lowers it (easier, better for climbing). Development simply tells you how far one full crank revolution rolls you forward.

Worked Example

A 50-tooth chainring with a 15-tooth cog on a 700c wheel (effective diameter ~26.3 in): ratio = 50 / 15 = 3.33, so gear inches = 26.3 × 3.33 = 87.7 gear inches. Development = 87.7 × π × 0.0254 = 7.0 m per crank revolution — a solid all-round road gear.

Gear Inches Quick Reference (700c wheel)

Why Use Gear Inches at All?

Raw gear ratios (chainring ÷ cog) ignore wheel size, so a 2:1 ratio feels very different on a 29-inch MTB wheel than on a 26-inch one. Gear inches folds wheel diameter back in, giving one number you can compare across any bike, wheel size, and drivetrain. It is the standard language for analyzing gear range and spacing.

Wheel Size Matters

The same gear ratio gives more gear inches on a larger wheel. That is why a mountain bike moving from 26″ to 29″ wheels effectively raises every gear, and why riders sometimes adjust their cassette to compensate. The calculator lets you pick your wheel size so the result reflects your actual bike.

Disclaimer: Gear inches uses an approximate effective wheel diameter that includes a typical tire; your exact figure shifts slightly with tire width and pressure. Use it as a comparison and planning tool rather than a precise physical measurement.