Bike Gear Ratio Calculator
Calculate gear inches for any chainring and cassette combination on your bike. Use it when choosing gearing for climbing, sprinting, or matching a new drivetrain setup.
About this calculator
Gear inches is the traditional imperial measure of how far a bicycle travels per crank revolution, originally derived from penny-farthing wheel diameters. The formula is: gear inches = (chainring / cassette) × (wheel diameter in mm / 25.4). The first part — chainring divided by cassette teeth — gives the mechanical gear ratio, meaning how many times the rear wheel turns for each full pedal revolution. Multiplying by wheel diameter (converted to inches) scales this to a real-world distance unit. A higher gear-inch value means more distance per pedal stroke but requires more force, favouring flat roads and sprints. A lower value requires less force and is easier to spin, making it ideal for climbing. Riders use gear inches to compare gearing across bikes with different wheel sizes on a common scale.
How to use
1. Enter your chainring teeth — for example, 50. 2. Enter your cassette teeth — for example, 17. 3. Enter your wheel diameter — for example, 622 mm (a standard 700c road wheel). 4. The calculator computes: (50 / 17) × (622 / 25.4) = 2.941 × 24.49 = 72.0 gear inches. This means each full pedal stroke propels you the equivalent of rolling a 72-inch wheel once. Compare this figure across gears to understand your spread from easiest to hardest.
Frequently asked questions
What is a good gear ratio for climbing hills on a road bike?
For steep climbs, most cyclists benefit from a gear producing 30–45 gear inches, which typically means a small chainring (34–36 teeth) paired with a large cassette sprocket (28–32 teeth) on a 700c wheel. Professional climbers often use compact or sub-compact cranksets specifically to access very low gearing on long alpine stages. For recreational riders tackling 8–10% gradients, a lowest gear of around 32–40 gear inches allows a sustainable cadence without excessive strain on the knees.
How does wheel size affect gear ratio calculations?
Larger wheels travel farther per revolution, so a given chainring-to-cassette ratio produces more gear inches on a 29-inch mountain bike wheel than on a 26-inch wheel. This is why gear-inches formulas must include wheel diameter — it normalises the comparison. When upgrading from 26-inch to 29-inch wheels, you effectively get a harder gear even if you keep the same drivetrain, and you may need to adjust your cassette to compensate and maintain similar climbing ability.
What is the difference between gear ratio and gear inches?
The gear ratio is simply the unitless number you get by dividing chainring teeth by cassette teeth — for example, 50/17 ≈ 2.94. It tells you how many times the rear wheel rotates per pedal stroke but says nothing about actual distance. Gear inches incorporates wheel size to translate that rotation into a real-world distance measurement, making it possible to compare gearing on bikes with different wheel diameters. Most serious cyclists and gear-selection tools prefer gear inches or development (metres per pedal stroke) for this reason.