Gear Inches Calculator
Calculate bicycle gear inches from chainring teeth, rear cog teeth and wheel diameter. Compare how tall or low a gear feels, see rollout per crank revolution and estimate speed at your cadence.
Enter Your Bike Setup
Advanced drivetrain option
How the Gear Inches Calculator Works
Gear inches combine your wheel size with the chainring-to-cog ratio so gears on different bikes can be compared on one scale. The value represents the diameter of an equivalent directly driven wheel that would travel the same distance for one crank revolution.
Add the tooth count of the front chainring and the rear cog you are using.
Use the outside diameter of the driven wheel including the inflated tire.
Lower gear inches favor easier climbing; higher gear inches favor more distance per pedal revolution.
Gear inches formula
Development formula
Development is the distance the bicycle travels for one complete crank revolution, assuming no tire slip.
Cadence speed formula
Gain ratio
Gain ratio also accounts for crank length. Because wheel radius and crank length use the same length unit, the result is dimensionless and can help compare bikes with different crank lengths.
Gear Inches Interpretation
There is no universal “best” gear-inch number. Terrain, rider strength, cadence, wheel size and riding style all matter. These bands are broad comparison guides, not performance requirements.
| Gear inches | General feel | Typical use |
|---|---|---|
| Below 25″ | Very low | Steep climbs, loaded touring, technical terrain |
| 25–40″ | Low | Climbing and easy spinning |
| 40–70″ | Moderate | Mixed terrain and comfortable cruising |
| 70–100″ | Tall | Road cruising and faster flat riding |
| Above 100″ | Very tall | High-speed riding, descents or sprint gearing |
Example Gear Inches Calculation
Suppose a bicycle uses a 50-tooth chainring, a 17-tooth rear cog and an overall wheel diameter of 26.3 inches.
Gear inches = 26.3 × 2.941 ≈ 77.4″
Development = 77.4 × π × 0.0254 ≈ 6.18 m/rev
At a cadence of 90 rpm, that development corresponds to roughly 33.4 km/h in an ideal no-slip calculation.
Frequently Asked Questions
What are gear inches?
Gear inches are a traditional bicycle gearing measure that combines wheel diameter and drivetrain ratio. Higher values indicate a taller gear, while lower values indicate an easier gear.
How do I calculate gear inches?
Multiply the driven wheel diameter in inches by the front chainring teeth divided by the rear cog teeth. For a standard derailleur drivetrain, the hub ratio is 1.
Should wheel diameter include the tire?
Yes. Gear inches depend on the actual rolling diameter, so including the inflated tire gives a more realistic result than using rim diameter alone.
What do higher gear inches mean?
Higher gear inches mean the bike travels farther per crank revolution but generally requires more force at the pedals at a given speed and cadence.
What do lower gear inches mean?
Lower gear inches provide easier mechanical gearing, which is useful for climbing, loaded riding and maintaining a comfortable cadence at lower speeds.
What is bicycle development?
Development is the distance traveled for one complete crank revolution. This calculator shows it in meters and feet per crank revolution.
What is gain ratio?
Gain ratio is a dimensionless bicycle gearing measure that includes crank length as well as wheel radius and drivetrain ratio. It is useful when comparing bicycles with different crank lengths.
Can I estimate speed from gear inches?
Yes. If cadence is known, development can be multiplied by crank revolutions per minute to estimate ideal road speed. Real speed can vary because of tire deformation, wheel diameter, coasting and riding conditions.