Bicycle Gear Ratio Converter

A bicycle gear ratio is the relationship between the number of teeth on the front chainring and the rear cog. It determines how far the bike travels per pedal revolution, how much effort is required to pedal, and ultimately how fast or easily the bike climbs hills. The gear ratio is calculated simply as chainring teeth divided by cog teeth: a 50-tooth chainring paired with a 17-tooth cog gives a ratio of 50/17 ≈ 2.94.

Understanding gear ratios helps cyclists optimize their setup for different riding styles. Road racers typically use larger chainrings (50-53 teeth) with small cogs (11-12 teeth) for high gear ratios that maximize speed on flat terrain. Mountain bikers prefer smaller chainrings (28-34 teeth) with large cogs (42-50 teeth) for low ratios that make steep climbs manageable. Track cyclists often use a single chainring and cog combination tuned for velodrome racing.

Beyond the basic ratio, this calculator computes several complementary metrics: gear inches (a traditional measure dating back to penny-farthings), development (distance per pedal revolution in meters), gain ratio (which accounts for crank length), and speed at any given cadence. Together, these metrics provide a complete picture of how a particular gear combination performs.

Several metrics describe bicycle gearing, each offering a different perspective on the relationship between pedaling effort and bike speed.

Each gear metric provides unique insights into how a gear combination behaves:

• Gear Ratio: The fundamental ratio of chainring to cog teeth. Higher means harder pedaling but more distance per revolution.
• Gear Inches: A traditional measure inherited from the penny-farthing era. It equals the gear ratio times the wheel diameter in inches. A gear inch value of 100 means the bike travels the same distance per pedal revolution as a penny-farthing with a 100-inch wheel.
• Development: The actual distance (in meters) the bike travels per complete pedal revolution. This is the most intuitive measure for comparing gears.
• Gain Ratio: Developed by Sheldon Brown, this measure accounts for crank arm length. It represents the ratio of the distance the pedal travels in one revolution to the distance the wheel travels.

The bicycle gear ratio calculator provides five inputs for comprehensive gear analysis:

1. Chainring teeth: Enter the number of teeth on your front chainring (or the large chainring for comparison purposes).
2. Cog teeth: Enter the number of teeth on your rear cog or sprocket.
3. Cadence (RPM): Enter your typical pedaling cadence in revolutions per minute.
4. Wheel diameter (BSD): Enter your wheel's bead seat diameter in millimeters (e.g., 700 for road, 622 for 29er MTB).
5. Tire width: Enter your tire width in millimeters to calculate the effective wheel circumference.

The results display gear ratio, gear inches, development, gain ratio, and speed at the specified cadence. Quick-select buttons for common road, MTB, and track setups are provided for easy configuration.

Gear ratio knowledge is essential for road cyclists optimizing their drivetrain. A standard road bike with 50/34 compact chainrings and an 11-28 cassette provides gear ratios from 1.21 (34/28) for steep climbs to 4.55 (50/11) for high-speed descents. Understanding which gear ratio to select at any given moment helps maintain an efficient cadence and conserve energy on long rides.

Mountain bikers face extreme terrain variations that demand wide gear ranges. A modern 1x12 drivetrain with a 30-tooth chainring and 10-51 tooth cassette provides ratios from 0.59 for grueling climbs to 3.0 for fast descents. The development metric is particularly useful here: at 0.59 ratio, each pedal revolution moves the bike only about 1.4 meters, making steep grades manageable.

Track cyclists use a single fixed gear ratio selected specifically for the velodrome event. Sprint events might use 51/14 (ratio 3.64), while endurance events use 49/15 (ratio 3.27). The fixed gear means the rider cannot coast, making cadence control and gear selection critical for both speed and safety.