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Physics

Verified calculator with a transparent formula

Physics

Bicycle Gear Ratio Calculator.

Calculates the gear ratio and gear inches for a bicycle drivetrain based on chainring and cassette sprocket sizes.

Results update live as you type.
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Your inputs

How it works

  1. 1

    Enter the number of teeth on your front chainring.

  2. 2

    Enter the number of teeth on your rear cassette sprocket.

  3. 3

    Enter your wheel diameter in inches.

  4. 4

    The calculator divides chainring teeth by cassette teeth to get the gear ratio, then multiplies by wheel diameter for gear inches.

chainring_teeth / cassette_teeth

Frequently asked questions

What does a higher gear ratio mean?

A higher gear ratio means more speed per pedal revolution but requires more effort. It's used for flat or downhill riding.

What is gear inches?

Gear inches is the effective diameter of the wheel in inches when accounting for the gear ratio. It helps compare gearing across different wheel sizes.

How do I choose the right gear ratio?

Choose a lower ratio for climbing and a higher ratio for speed. Consider your fitness level and terrain.

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Results

Formula checked

Gear ratio

3.125

Gear inches85.9in
Ask Anything

Estimate for general guidance only — verify important decisions with an appropriate professional.

How it works

Calculates the gear ratio and gear inches for a bicycle drivetrain based on chainring and cassette sprocket sizes.

  1. Enter the number of teeth on your front chainring.
  2. Enter the number of teeth on your rear cassette sprocket.
  3. Enter your wheel diameter in inches.
  4. The calculator divides chainring teeth by cassette teeth to get the gear ratio, then multiplies by wheel diameter for gear inches.

Formulas

The math behind this calculator, written out so you can verify the result.

Gear Ratio

Gear Ratio = Chainring Teeth / Cassette Teeth

This is the number of times the rear wheel turns for each full pedal crank revolution.

Gear Inches

Gear Inches = Gear Ratio × Wheel Diameter

This converts the gear ratio into an equivalent wheel diameter, making it easier to compare different bikes.

Real-world use cases

Where this calculation shows up in everyday life.

Bike Setup

Determine the best gear combination for your riding style and terrain.

Example: Choose a 34/28 for climbing steep hills.

Comparing Bikes

Compare the gearing of different bikes regardless of wheel size.

Example: A 50/16 on 27.5" wheels vs a 48/15 on 29" wheels.

Training

Plan gear ratios for interval training or endurance rides.

Example: Use a higher ratio for sprint intervals.

Tips and common mistakes

Tips

  • For climbing, aim for a gear ratio below 1.5.
  • For flat terrain, a ratio between 2.5 and 3.5 is common.
  • Larger wheels require a slightly higher gear ratio to achieve the same gear inches.
  • Test different ratios to find what feels comfortable.

Common Mistakes to Avoid

  • Forgetting to include wheel diameter when comparing bikes.
  • Using the wrong teeth count (e.g., counting the chainring bolts).
  • Assuming a higher gear ratio is always better.

Assumptions and limitations

  • Use the stated inputs and units.
  • Results are estimates for planning and education.
  • Check measurements and source data before making an important decision.