How do you calculate gear inches?

Multiply the wheel diameter in inches by the chainring teeth and divide by the cog teeth. A 27 inch wheel with a 39 × 14 gear gives 27 × 39 ÷ 14 = 75.2 gear inches. Higher numbers are harder, faster gears.

What is metres of development?

Development is how far the bike travels for one full turn of the cranks: wheel circumference in metres × chainring ÷ cog. A 622 mm rim with a 33 mm tire (688 mm wheel) in 52 × 13 travels about 8.64 m per crank turn.

Gain ratio divides the distance the bike moves by the distance the pedal moves in a circle: (wheel radius ÷ crank length) × chainring ÷ cog. With a 340 mm wheel radius and 170 mm cranks, 53 × 19 gives 2.0 × 53 ÷ 19 = 5.58. Unlike gear inches, it accounts for crank length.

How is bike speed calculated from cadence?

Speed in km/h = development in metres × cadence in rpm × 60 ÷ 1000. A 700×25c wheel in 50 × 11 develops about 9.60 m, so 90 rpm gives roughly 51.8 km/h (32.2 mph). Real speed also depends on wind, gradient and power, so treat it as the speed that gear and cadence produce.

How is wheel diameter worked out from tire size?

The calculator adds twice the tire width to the rim bead-seat diameter, for example 622 + 2 × 28 = 678 mm for 700×28c. Actual tires vary with brand, pressure and rim width, so if you have measured your wheel roll-out, choose Custom and enter that diameter.

What gear ratio is good for climbing?

Many riders want a lowest gear near or below 1:1 (about 27 gear inches on a 700c road bike) for steep climbs, and lower still on loaded touring or mountain bikes. The right number depends on fitness, load and gradient, so compare your current lowest gear with what has felt too hard.

Bicycle Gear Calculator

Build a gear chart for any chainring and cassette combination: gear inches, gain ratio, development in metres and speed at a chosen cadence.

Gear inches = wheel diameter in inches × chainring teeth ÷ cog teeth.

Drivetrain

Chainrings (teeth) Cassette cogs (teeth) Wheel and tire

Crank length (mm)

Cadence (rpm)

Chart shows

Gear chart

Rows are cogs, columns are chainrings.

Building wheels for this bike? Work out spokes with the spoke length calculator and check the build with the spoke tension calculator.

Quick answer

Gear inches = wheel diameter in inches × chainring teeth ÷ cog teeth. Development (metres per crank turn) = wheel circumference in metres × chainring ÷ cog. Gain ratio = (wheel radius ÷ crank length) × chainring ÷ cog. Speed in km/h = development × cadence × 60 ÷ 1000.

Examples

Gear (700×28c, 170 mm cranks, 90 rpm)	Gear inches	Development	Gain ratio	Speed
50 × 11	121.3	9.68 m	9.06	52.3 km/h
34 × 28	32.4	2.59 m	2.42	14.0 km/h

Enter your chainrings and cassette to chart every gear.

Summary

Enter one to three chainrings and a list of cassette cogs, pick a wheel and tire size (or type a wheel diameter), and set crank length and cadence. The calculator builds a chart of every combination in the unit you choose: gear inches, metres of development, gain ratio, plain ratio, or road speed in km/h or mph. Wheel diameter is estimated as rim bead-seat diameter plus twice the tire width, the same approximation used in common gear-inch tables. Everything runs in your browser.

How it works

Enter your chainring tooth counts, for example 50, 34 for a compact road double.
Pick a cassette preset or type the cog sizes, smallest to largest.
Choose the wheel and tire size, or select Custom and enter the wheel diameter in millimeters.
Set crank length (needed for gain ratio) and the cadence you want speeds for.
Choose what the chart shows: gear inches, development, gain ratio, ratio or speed.
Read the chart across a row to compare chainrings, or down a column to see the steps between cogs.

Use cases

Compare a compact 50/34 crankset with a 52/36 before buying.
Check whether a wider cassette gives a low enough climbing gear.
Pick a single-speed or fixed-gear ratio by gear inches.
See the speed you reach at 90 rpm in your top gear.
Compare gearing across 700c, 29er, 27.5 and 26 inch wheels.
Spot duplicate gears between the big and small chainring.

Frequently Asked Questions

Last updated: 2026-10-08 · Reviewed by Nham Vu