Bicycle Gear Inch Calculator

Also calculates metres of development and (optionally) speed or cadence, and gain ratio

Select rear tyre size   700 x 18C 700 x 23C 700 x 25C 700 x 28C 700 x 32C 700 x 35C 700 x 37C ------------------ 29er x 1.25" 29er x 1.5" 29er x 1.75" 29er x 1.95" 29er x 2.125" 29er x 2.35" ------------------ 26 x 1.25" 26 x 1.5" 26 x 1.75" 26 x 1.95" 26 x 2.125" 26 x 2.35" ------------------ 20 x 1.125" 20 x 1.35" 20 x 1.5" 20 x 1.75" 20 x 1.95" ------------------ 18 x 1.5" 18 x 1.75"
 Number of chainring teeth (front cog)
 Number of sprocket teeth (rear cog)
 Pedaling cadence (rpm) (optional)
 Speed (mph) (optional)
 Crank length (millimetres) (optional)

Bicycle 'gear inches' is equivalent to the diameter of the drive wheel on a direct-drive bicycle with pedals fixed to the wheel, or when the number of teeth on the chainring and the sprocket are the same: a 1 to 1 drive. Gear inches is used mostly for comparing one drive train ratio to another and has little physical basis on a bicycle with derailleur gears.

Metres of development has a physical basis: distance travelled with one turn of a crank.

Gain ratio is distance travelled divided by the circular distance travelled by a pedal.

Typical crank lengths: 170mm on road bikes and 175mm on mountain bikes.

Gear inch calculator by Patrick Taylor