Gear Inches Calculator

This builds the gear inch chart for a whole drivetrain rather than a single ratio. Enter your chainrings, every cog on the cassette, the rim size and the tire width, and it returns a table of gear inches for each combination, plus metres of development, gain ratio and speed at a cadence you choose. It also reports the range from lowest to highest, how many combinations are genuinely different rather than duplicates of each other, and the biggest jump between neighbouring gears. The tire is assumed to be as tall as it is wide, which is close on a road tire and a few percent optimistic on a wide MTB tire.

Tire Width In

Millimetres Inches

Road, gravel and touring tires are marked in millimetres. Mountain, BMX, folder and childrens tires are marked in inches, so enter 2.35 rather than working out that it is 60 mm.

Chainring Teeth (front) *

One to three numbers separated by commas. A compact road double is 50,34; a 1x is a single number such as 32.

Cassette or Freewheel Cogs (rear) *

Up to 14 numbers, smallest to largest or the other way round. Printed on the cassette box as 11-28 with the sprockets listed.

Rim Size (ISO bead seat diameter)

Tire Width (mm) *

From the sidewall. 700x28c means 28 in millimetres; 29x2.35 means 2.35 in inches.

Crank Length (mm)

Only the gain ratio column uses this. Stamped on the back of the crank arm.

Cadence for the Speed Figures (rpm)

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