⚙️ Bike Gear Ratio Calculator
Enter chainring, cassette sprockets, and wheel size to generate a complete gear chart.
Separate values with commas. They will be sorted automatically.
Gear Table
| Sprocket (T) | Gear Ratio | Gear Inches | Rollout (m) | Speed @ 90 rpm (km/h) |
|---|---|---|---|---|
| 11 | 4.73 | 130.0 | 10.37 | 56.0 |
| 13 | 4.00 | 110.0 | 8.78 | 47.4 |
| 15 | 3.47 | 95.3 | 7.61 | 41.1 |
| 17 | 3.06 | 84.1 | 6.71 | 36.2 |
| 19 | 2.74 | 75.3 | 6.01 | 32.4 |
| 21 | 2.48 | 68.1 | 5.43 | 29.3 |
| 24 | 2.17 | 59.6 | 4.75 | 25.7 |
| 28 | 1.86 | 51.1 | 4.08 | 22.0 |
How to Use This Calculator
Input drivetrain
Enter the chainring and cassette sprocket teeth counts.
Select wheel size
Choose standard wheel diameter or specify a custom one.
Set cadence
Use your target cadence to see real-world speeds for each gear.
Review gear table
Compare gear inches, rollout distance, and cadence-based speeds.
Formula
Gear Inches = Wheel Diameter (in) × (Chainring ÷ Sprocket)
Rollout distance per pedal stroke equals gear inches × π × 0.0254. Speed in km/h uses rollout × cadence × 60 ÷ 1000. These metrics help compare gearing between different bikes.
Example
For a 700c wheel (27.5 in) with 52/15 gearing: gear inches = 27.5 × (52/15) = 95.3. Rollout ≈ 7.55 m. At 95 rpm, speed ≈ 43.0 km/h.
Variables
- Wheel diameter: Tyre plus rim
- Chainring/sprocket: Drivetrain teeth
- Cadence: Pedal revolutions per minute
Understanding Gear Charts
Gear charts help riders visualize how each gear feels on different terrain. Gear inches allow easy comparisons between drive trains; rollout informs track sprinters and fixed-gear riders.
Use Cases
- Road cyclists planning cassette swaps before hilly races.
- Triathletes optimizing cadence to maintain aero efficiency.
- Track racers choosing gear combos for specific velodrome lengths.
Tips
- Create a laminated gear table for your stem or smart trainer dashboard.
- Record your preferred cadence/speed pairings during workouts.
- Remember tyre changes or wheel swaps alter rollout metrics.
Frequently Asked Questions
What are gear inches?
Gear inches express wheel travel per crank revolution relative to a high-wheeler bike. Higher values mean harder gears.
Why does cadence matter?
Cadence and gear ratio together set your speed. Efficient riders choose cadence that suits their physiology.
Should I round gear ratios?
Keep multiple decimal places for analysis. Small differences can matter when comparing similar cassettes.
How do compact cranksets impact the table?
Use the calculator with 50/34 chainrings to see reduced top-end gears and easier climbing ratios.
Can I input multiple chainrings?
Run the calculator separately for each chainring to generate individual tables, then merge them for a complete chart.