Bicycle Gear Ratio Calculator
Calculate bicycle gear ratio, gear inches, and development (distance traveled per pedal revolution) from chainring teeth, cog teeth, and wheel size — 700c, 650b, 26", 29er, or a custom diameter.
Input
Tooth count of the front chainring.
Tooth count of the rear cog/sprocket.
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
Work out how "hard" or "easy" a specific gear on your bike actually is. Enter the number of teeth on your chainring (front) and cog or sprocket (rear), pick a wheel size, and the calculator instantly returns the gear ratio, gear inches, and the development — the distance your bike travels for one full pedal revolution.
What the numbers mean
Gear ratio is simply chainring teeth divided by cog teeth. A 50-tooth chainring paired with a 17-tooth cog gives a ratio of 50 ÷ 17 = 2.94 — for every pedal stroke, the rear wheel spins 2.94 times. Higher ratios mean a harder, faster gear; lower ratios mean an easier, slower-spinning gear for climbing.
Gear inches is a traditional cycling measurement dating back to penny-farthings with direct-drive front wheels. It's calculated as wheel diameter (in inches) × gear ratio, and lets you compare gearing across completely different bikes and wheel sizes on one scale. Typical road gears fall somewhere between 30″ (easy climbing) and 110″ (fast descending); a 50/17 combination on a 700c wheel works out to about 79.4″.
Development (also called "rollout") is the actual ground distance covered per pedal revolution — wheel circumference × gear ratio — shown here in both feet and meters. It's the metric velodrome and touring cyclists use to plan cadence against target speed, since it converts directly into a real-world distance rather than an abstract ratio.
How to use it
- Enter your chainring's tooth count.
- Enter your rear cog or sprocket's tooth count.
- Choose your wheel size — 700c (road), 650b, 26″ (mountain bike), or 29er — or select "Custom diameter" to enter an exact rolling diameter in inches (including the tire).
- Results update instantly: gear ratio, gear inches, wheel circumference, and development per pedal stroke.
Run the calculation again for each chainring/cog combination on your bike (e.g. your smallest and largest gears) to see the full range your drivetrain covers.
FAQ
Why does wheel size matter if the gear ratio is the same? Gear ratio alone only tells you the mechanical relationship between chainring and cog — it says nothing about how far the bike actually moves. A 2.94 ratio on a small-wheeled folding bike covers much less ground per pedal stroke than the same ratio on a 700c road wheel, because the wheel circumference is smaller. Gear inches and development both factor wheel size back in.
What wheel diameter should I use for "custom"? Measure the outer rolling diameter of the wheel with the tire mounted and inflated, in inches. If you only know the circumference, divide it by π (≈3.14159) to get the diameter.
Is 700c always exactly 27 inches? No — actual 700c rolling diameter varies slightly with tire width (roughly 26.6″–27.3″ depending on the tire). This calculator uses 27″ as a standard road-tire approximation; use "Custom diameter" for a precise figure.
Does this account for tire pressure or rider weight? No — those change the rolling diameter by only a fraction of a percent and aren't part of standard gear-inch/development calculations.
Privacy
All calculations run entirely in your browser (and identically via the API) — no bike data, tooth counts, or wheel sizes are stored or sent anywhere beyond the calculation itself.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/bicycle-gear-ratio-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"chainringTeeth": "50",
"cogTeeth": "17",
"wheelSize": "700c",
"customWheelDiameter": ""
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `bicycle-gear-ratio-calculator` tool (Bicycle Gear Ratio Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.