Cycling Gear Ratio Calculator: Gear Inches and Speed

Bicycle gearing, cadence and rollout tool

Bicycle Gear Calculator

Use this cycling gear ratio calculator to build a bicycle gear chart from one or more chainrings and rear cogs. Calculate gear inches, development, gain ratio, speed at cadence and the cadence required for a target speed.

Measured rollout is more accurate than the nominal tire label.
Effective outside diameter in inches.
Enter 1 to 4 whole tooth counts, separated by commas.
Enter 1 to 20 whole tooth counts, separated by commas.
Used for gain ratio; measure from bottom-bracket center to pedal-spindle center.
Speed assumes no tire slip and a constant cadence.

Gear chart results

ChainringRear cogRatioGear inchesDevelopmentGain ratioSpeedCadence at target

Bicycle gear formulas

Gear ratio = front chainring teeth ÷ rear cog teethGear inches = effective wheel diameter in inches × gear ratioDevelopment = π × effective wheel diameter × gear ratioGain ratio = wheel radius ÷ crank length × gear ratioSpeed = development × cadence × 60

Gear inches compare how far a bicycle advances for a given crank rotation using the diameter of an equivalent direct-drive wheel. Development states the actual distance traveled per crank revolution. Gain ratio also includes crank length, so it is dimensionless and can compare bicycles with different cranks.

50 teeth
→
17
→
27 in wheel

Checked example

A 50-tooth chainring, 17-tooth rear cog and 27-inch effective wheel produce a 2.941:1 ratio, 79.41 gear inches and 6.337 meters of development. With 172.5 mm cranks, gain ratio is 5.847. At 90 RPM the theoretical speed is 34.22 km/h (21.26 mph); holding 25 km/h requires about 65.75 RPM.

How to measure the wheel accurately

Nominal labels such as 700C, 29 inch and 27.5 inch do not guarantee the tire’s loaded outside diameter. Tire width, rim width, pressure, tread and rider load change rollout. For the closest estimate, mark the floor and tire, roll the loaded bicycle through one full wheel revolution, measure the distance in millimeters and choose measured circumference.

Reading the chart

  • Lower gear inches and development make climbing and starting easier but reduce distance per pedal revolution.
  • Higher values increase rollout and theoretical speed at the same cadence but require more pedal force at the same wheel resistance.
  • Cadence at target speed helps compare which combination places a planned pace inside a comfortable cadence range.
  • Overlapping combinations can have similar ratios even when they use different chainrings and cogs.

Limits and real-world differences

The speed result is kinematic, not a performance prediction. It assumes constant cadence, no wheel slip and the entered loaded rollout. It does not account for aerodynamic drag, gradient, wind, rolling resistance, drivetrain losses, tire growth, freehub behavior, shifting time or the rider’s sustainable power.

This calculator does not verify derailleur capacity, chain length, chainline, frame clearance, sprocket compatibility, hub standards or safe component combinations. Confirm component limits with the bicycle and drivetrain manufacturers before changing gearing.

Related calculators

Use the Gear Ratio Calculator for general gear, sprocket and vehicle drivetrains, the Power-to-Weight Ratio Calculator for cycling W/kg, the Circumference and Diameter Calculator for a single wheel conversion, or the Speed Conversion Calculator for pace and speed units.