⚙️ Bike Gear Ratio Calculator
Enter your chainring and cog teeth and pick a wheel size to see the gear ratio, gear inches, development per pedal stroke, and the speed you'd ride at your chosen cadence.
Great for comparing gears across road, gravel and mountain setups.
🧮 Work Out Your Gearing
⚙️ Your gear
| Gear inches | 94.3″ |
| Development (metres / rev) | 7.52 m |
| Speed at 90 rpm | 40.6 km/h |
Understand every gear on your bike
The same cog swap feels completely different on a compact chainring than on a big one, and gear inches let you compare them fairly. Whether you're choosing a climbing cassette, sizing a single-speed, or working out why you spin out on descents, it all comes back to the ratio between the teeth up front and out back.
This calculator turns those tooth counts and your wheel size into ratio, gear inches, development and speed — so you can dial in gearing before you spend money on parts. See exactly how each figure is derived in the FAQ.
❓ Frequently Asked Questions
How do I calculate a bike gear ratio?
Gear ratio is simply the number of teeth on the front chainring divided by the number of teeth on the rear cog. A 50-tooth chainring with a 14-tooth cog gives 50 ÷ 14 = 3.57, meaning the rear wheel turns 3.57 times for every single turn of the pedals. A higher ratio is a harder, faster gear; a lower ratio is an easier gear for climbing.
What are gear inches and development?
Gear inches is a classic way to compare gears across different wheel sizes: it's the gear ratio multiplied by the wheel diameter in inches, effectively the diameter of the equivalent direct-drive wheel. Development (or 'rollout') is how far the bike travels for one full pedal revolution — the gear ratio times the wheel's circumference in metres. Both let you compare, say, a 700c road gear against a 26-inch mountain-bike gear on equal terms.
How is speed worked out from gearing and cadence?
Speed is development multiplied by cadence: each pedal revolution rolls you 'development' metres, and cadence tells you how many revolutions per minute. The calculator multiplies development (m) by cadence (rpm) by 60 and divides by 1000 to give kilometres per hour. It assumes you hold that cadence steadily in the chosen gear, with no coasting.
Which wheel diameter should I choose?
Pick the preset that matches your wheels: 700c covers most road and gravel bikes (about 26.4 inches including tyre), 650b/27.5-inch is common on gravel and modern mountain bikes, 29er is the tall MTB standard, and 26-inch is the classic mountain-bike size. Tyre width shifts the true diameter slightly, so treat gear inches and speed as close estimates rather than exact figures.