Bike Gear Ratio Calculator
Calculate the gear ratio, gear inches, and speed for a given chainring and sprocket combination. Useful for cyclists to optimize cadence and performance.
Published by:
isCalculator Editorial Team
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How to use this tool?
This calculator computes key metrics for your bicycle's drivetrain based on chainring and sprocket teeth, wheel diameter, and cadence.
- Enter Chainring Teeth – The number of teeth on your front gear (e.g., 50). Must be a positive integer.
- Enter Sprocket Teeth – The number of teeth on your rear cassette (e.g., 12). Must be a positive integer.
- Set Wheel Diameter (inches) – Default is 27.5 inches. Adjust for your wheel size (e.g., 26, 29, 700c ≈ 27.5).
- Set Cadence (RPM) – Your pedaling revolutions per minute. Default is 90 RPM.
- Click Calculate to see results.
Outputs explained:
- Gear Ratio – Chainring teeth ÷ sprocket teeth. Higher = harder to pedal, more speed.
- Gear Inches – Gear ratio × wheel diameter. A traditional measure of effective wheel size.
- Speed (mph) – Estimated speed based on gear inches, cadence, and wheel circumference.
All inputs use imperial units (inches, RPM). Ensure your values are positive numbers.
Previous Results
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Frequently Asked Questions
Gear ratio is the number of teeth on the chainring divided by the number of teeth on the rear sprocket. It determines how many times the rear wheel turns for each pedal revolution.
Gear inches is a measure of how far the bike travels per pedal revolution, calculated as gear ratio multiplied by wheel diameter in inches.
Speed (mph) = gear inches × π × cadence (RPM) × 60 minutes per hour / 63360 inches per mile.
