Gear Inches Calculator (Cycling)
Calculate gear inches from chainring teeth, cog teeth, and wheel diameter.
Compare bike gearing across road, mountain, and gravel setups.
Gear Inches
Gear inches is the traditional way cyclists compare gearing across bikes with different wheel sizes, chainrings, and cogs. The number tells you the diameter (in inches) of a directly-driven wheel that would travel the same distance per crank revolution.
Formula
gear inches = (chainring teeth ÷ cog teeth) × wheel diameter (inches)
Higher gear inches = harder to push, faster top speed. Lower gear inches = easier to push, better for climbing and slow-speed control.
Worked Example — 50/12 with 700×25c Wheel
A typical 700c road wheel with a 25 mm tire has an effective diameter of about 26.7 inches.
- Gear inches = (50 / 12) × 26.7 ≈ 111.3 in
That is a fast top gear suited to descending or pacelines.
Common Reference Ranges
| Use | Approx. Gear Inches |
|---|---|
| Mountain bike easiest gear | 18–22 |
| Touring loaded climber | 20–28 |
| Road bike easiest gear | 28–40 |
| Road bike middle gear | 60–75 |
| Road bike hardest gear | 100–120 |
| Track / sprint | 90–105 |
Wheel Diameter Cheat Sheet
| Tire Size | Diameter (in) |
|---|---|
| 700×23c | 26.4 |
| 700×25c | 26.7 |
| 700×28c | 27.0 |
| 650b × 47 (gravel) | 27.0 |
| 27.5" mountain | 27.5 |
| 29" mountain | 29.0 |
| 26" classic MTB | 26.0 |
Why Not Just Use Ratio?
Two bikes with identical 50/12 ratios but different wheel sizes (a 26" mountain bike vs a 700c road bike) feel completely different. Gear inches normalizes that — a 100 gear-inch top is the same effort and speed regardless of wheel size.
Modern Alternative — Development
European cyclists often use development (meters per crank revolution) instead of gear inches. Development = π × wheel diameter (m) × ratio. Both convey the same information; gear inches remain dominant in U.S. and U.K. cycling culture.