Bike Gear Inches Calculator

About this calculator

Gear inches is a unit dating back to the penny-farthing era, when a bike’s gearing really was defined by its front wheel diameter; today it’s calculated as wheel diameter × (chainring teeth ÷ cog teeth), giving an equivalent wheel size that lets you compare gearing across completely different bike setups — a modern bike’s gear-inch number tells you what size direct-drive wheel would feel equivalent to its current gear.

Cyclists and bike mechanics use gear inches to compare gearing consistently across bikes with different wheel sizes, chainring counts, or drivetrain types, since simply comparing chainring-to-cog ratios doesn’t account for how wheel diameter changes how far the bike actually travels per pedal stroke. It’s especially useful when swapping between bikes with 26-inch, 700c, or 29-inch wheels, or when setting up a new drivetrain to match a rider’s preferred gearing feel from a previous bike.

This calculator takes your wheel diameter, chainring teeth, and cog teeth and returns the resulting gear inches.