Bike Gear Calculator
Find gear inches and development from your gearing.
Gear inches let you compare gearing across bikes and wheel sizes.
How the Math Works
Gear inches is a fundamental measurement in bicycle gearing that represents the effective wheel diameter if your bike were equipped with a single large tire driven directly by the chain. The formula gear inches = (chainring ÷ cog) × wheel diameter calculates this by taking the ratio of your chainring teeth to cog teeth, then multiplying by your wheel diameter. For example, a 48-tooth chainring paired with a 16-tooth cog on a 27-inch wheel yields (48÷16)×27 = 81 gear inches. This ratio tells you how many times the wheel would rotate for each crank revolution.
Practical Applications
To use this calculator practically, first measure your wheel diameter - typically 26, 27, or 29 inches for most bikes, or calculate it from rim width plus twice the tire height. Count the teeth on both your chainring (the front sprocket) and cog (the rear sprocket). Input these values into the formula or our calculator to determine your gear inches. You can also rearrange the formula to work backwards - if you know your desired gear inches and wheel size, you can solve for the required chainring-to-cog ratio. For development, multiply gear inches by π to get the distance your bike travels per crank revolution in inches.
Day-to-Day Use
Understanding your gear inches helps you make informed decisions about bike setup and riding efficiency. Knowing your low gear ratio is crucial for tackling steep hills without excessive pedaling strain, while your high gear determines how fast you can maintain momentum on flat terrain. Cyclists use this information when selecting gear ratios for different purposes - a mountain bike needs lower gear inches for climbing, while a road bike benefits from higher ratios for speed. The development measurement tells you exactly how far you'll travel per pedal stroke, helping you estimate timing for sprints, plan rest stops, or simply understand why certain gears feel easier or harder on longer rides.
Worked example
50/14, 27 in wheel → 96.4 gear inches.
FAQ
Higher gear inches?
A harder, faster gear (more distance per pedal stroke).