Gear inches and development describe how “big” a gear is regardless of how it’s made up. A 50/17 on a road bike and a 34/11 give similar gears – which this calculator makes obvious.
How to use the Bike Gear Calculator
- Wheel (rim bead seat diameter, mm)
- Custom bead seat diameter (mm)
- Tyre width (mm)
- Chainring teeth
- Cog teeth
- Crank length
- Smallest chainring
- Largest chainring
- Smallest cog
- Largest cog
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the chainring and cog, the wheel and tyre, the crank length, and your drivetrain’s smallest and largest chainrings and cogs.
Inputs explained
| Field | What to enter |
|---|---|
| Wheel (rim bead seat diameter, mm) | Choose one: 700c / 29″ (ISO 622), 650b / 27.5″ (ISO 584), 26″ MTB (ISO 559), 27″ old road (ISO 630) … |
| Custom bead seat diameter (mm) | A number |
| Tyre width (mm) | A number |
| Chainring teeth | A number |
| Cog teeth | A number |
| Crank length | Units: mm, in |
| Smallest chainring | A number |
| Largest chainring | A number |
| Smallest cog | A number |
| Largest cog | A number |
What each result means
- Gear ratio = [Chainring teeth]÷[Cog teeth]
- Gear range = [Largest chainring]÷[Smallest cog]÷([Smallest chainring]÷[Largest cog])×100
Example values
How the main result changes when Custom bead seat diameter changes and everything else stays at the example values above:
| Custom bead seat diameter (mm) | Gear inches (in) |
|---|---|
| 311 | 78.5 |
| 466.5 | 78.5 |
| 622 | 78.5 |
| 777.5 | 78.5 |
| 933 | 78.5 |
| 1,244 | 78.5 |
Formula
Ratio = F ÷ R · Gear inches = ratio × wheel diameter (in) · Development = ratio × circumference · Gain ratio = (wheel radius ÷ crank length) × ratio
Worked example
Inputs — Wheel (rim bead seat diameter, mm): 700c / 29" (ISO 622); Tyre width (mm): 28; Chainring teeth: 50; Cog teeth: 17; Crank length: 172.5 mm; Smallest chainring: 34; Largest chainring: 50; Smallest cog: 11; Largest cog: 32.
Results — Gear ratio = 2.941; Gear inches = 78.5 in; Development (distance per pedal turn) = 6.2647 m; Gain ratio = 5.78; Speed at 90 rpm = 33.83 km/h; Lowest gear = 28.4 gear inches; Highest gear = 121.3 gear inches; Gear range = 428 %.
Key terms
- Development
- Distance travelled per pedal revolution.
Frequently asked questions
What are gear inches?
The diameter of an old high-wheeler that would travel as far per pedal turn.
What is a good low gear for climbing?
Under about 30 gear inches for steep climbs with a load.
What is the gain ratio?
Wheel travel per crank-arm travel – it includes crank length.
What does gear range mean?
Highest gear ÷ lowest gear; 400–500% suits touring and gravel.