⚙️ Gear Ratio & Gear Inches Calculator
Calculate your bicycle's gear ratio and gear inches (a standard way of comparing gearing across different wheel sizes) from chainring and cog tooth counts.
Ratio, then gear inches
gear ratio = chainring teeth / cog teeth
gear inches = gear ratio × wheel diameter (in)A 50t ring with a 25t cog is exactly 2.00:1 - the wheel turns twice per pedal revolution. On a 27 in wheel that is 54.0 gear inches, meaning the bike behaves like a penny-farthing with a 54 in driven wheel. Multiply gear inches by π for the roll-out: 169.6 in, or 4.31 m, of road per pedal turn.
Which wheel diameter to enter
Measure the outside of the inflated tyre, not the rim. Common figures:
| Wheel and tyre | Diameter |
|---|---|
| 700 × 25c road | 26.4 in |
| 700 × 32c | 26.9 in |
| 650b / 27.5 × 2.1 | 27.5 in |
| 29 × 2.2 MTB | 29.0 in |
The 27 in default is the old nominal road size and reads about 0.6 in high for a modern 700c wheel, which shifts the answer by roughly a gear inch.
- Below about 30 gear inches is granny-gear territory for steep loaded climbs; 50-70 is normal cruising; 100-120 is a road top gear.
- Ratios compare drivetrains only. Gear inches compare bikes, because it folds in the wheel - the same 2:1 is 54 in on a road bike and 58 in on a 29er.
Frequently asked questions
What is a 50/25 gear in gear inches?
2.00:1, which on a 27 in wheel is 54.0 gear inches and rolls 4.31 m per pedal revolution. On a measured 26.4 in road wheel the same gear is 52.8 in.
What are gear inches on a bike?
The diameter of the direct-drive wheel that would give the same gearing. It came from penny-farthing days, and survives because one number captures chainring, cog and wheel size together.
Is a higher gear ratio harder to pedal?
Yes. A bigger ring or a smaller cog raises the ratio, so the wheel turns further per pedal stroke and each stroke takes more force. 34/32 at 1.06:1 is a climbing gear; 50/11 at 4.55:1 is a descending gear.