Bike Gear Inches Calculator
See your gearing in gear inches.
Result
How it is calculated
Gear inches is the diameter of the drive wheel multiplied by the gear ratio between the front chainring and the rear cog. It gives the size of an old-style direct-drive wheel that would feel the same.
gear inches = wheel diameter × chainring teeth ÷ cog teeth
wheel diameter is the outer diameter of the inflated wheel including the tyre, in inches (decimals such as 27.5 are fine). chainring teeth is the tooth count of the front ring and cog teeth the tooth count of the rear sprocket in use. All three must be above zero, and the two tooth counts must be whole numbers: 50.5 teeth shows no result. The answer is shown to 1 decimal. A larger number is a harder gear that moves the bike further per pedal turn; a smaller one is easier and suits climbing. The tool handles one chainring and cog pair at a time, so check each combination separately.
Worked example
A road bike has a wheel of 27 in, a 50-tooth chainring and a 14-tooth cog. Gear ratio: 50 ÷ 14 ≈ 3.571. Multiply by the wheel diameter: 27 × 3.571. The gear is 96.4 gear inches. In the easiest combination, a 34-tooth ring with a 28-tooth cog, the same wheel gives 27 × 34 ÷ 28 ≈ 32.8, a much lighter gear for climbing.
Common mistakes
- Entering the wheel size in millimetres (622) or in the wheel's marked size, such as 700c. The field is the overall diameter in inches, around 27 for a 700c road wheel with a tyre.
- Swapping chainring and cog. The front ring is the numerator, so 14 ÷ 50 would give a tiny gear.
- Treating gear inches as a distance. It is a measure of gearing; the distance per pedal turn is gear inches × π, in inches.
- Ignoring the tyre. A wide tyre makes the wheel diameter larger, which raises the gear inches slightly for the same teeth counts.
- Entering a fractional tooth count, such as 50.5, or a zero cog. Teeth are whole numbers above zero, and anything else gives no result.
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.
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