Bike Gearing Ratio Calculator
Use this tool to calculate gear ratio, gear inches, rollout distance, and estimated speed at your cadence.
What is a bike gearing ratio?
A bike gearing ratio tells you how many times the rear wheel turns for one full revolution of the pedals. It is one of the most useful numbers for understanding how “hard” or “easy” a gear feels.
The formula is simple: Gear Ratio = Front Chainring Teeth ÷ Rear Cog Teeth. A higher ratio means more speed potential at the same cadence, while a lower ratio means easier climbing.
Why gearing ratio matters
- Climbing: Lower gear ratios reduce pedal force and help you stay seated on steep grades.
- Flat speed: Higher ratios let you travel farther per pedal stroke.
- Cadence control: Better gearing keeps your cadence in an efficient range.
- Bike setup decisions: Helps choose chainrings and cassette sizes that match your terrain.
How this calculator works
1) Gear ratio
Calculated directly from front and rear tooth counts.
2) Gear inches
Gear inches are a traditional way to compare effective gearing: Gear Inches = Gear Ratio × Wheel Diameter (inches). Larger gear inches mean a harder, faster gear.
3) Development (rollout)
Development is the distance traveled for one pedal revolution: Wheel Circumference × Gear Ratio. This is shown in meters per crank revolution.
4) Estimated speed
Speed is estimated from your cadence and development, then displayed in km/h and mph. It is a no-slip theoretical speed, so real-world conditions (wind, gradient, tire pressure, drivetrain losses) will reduce it.
Practical gearing tips by riding style
Road cycling
A common setup is 50/34 chainrings with an 11–30 or 11–34 cassette. This gives high-end speed and low-end climbing support.
Gravel and all-road
Riders often choose smaller chainrings and wider-range cassettes for mixed surfaces, where cadence changes frequently and traction can limit usable torque.
Mountain biking
Modern MTB drivetrains usually use a single front ring (e.g., 30T or 32T) paired with a wide cassette (e.g., 10–51). Low ratios are valuable for steep, technical climbing.
Example calculation
Suppose you run a 48T chainring, 16T rear cog, and a 27" wheel at 85 rpm:
- Gear ratio = 48 / 16 = 3.00
- Gear inches = 3.00 × 27 = 81.0"
- Development ≈ 6.46 m/rev
- Estimated speed ≈ 33.0 km/h (20.5 mph)
How to choose better gears for your goals
- If climbs feel too hard, reduce your lowest gear ratio (smaller front ring, larger biggest rear cog, or both).
- If you spin out on descents, increase your top gear ratio (larger front ring or smaller smallest rear cog).
- Keep your preferred cadence in mind—many riders perform best around 80–100 rpm.
- Use actual loaded wheel diameter if you want higher accuracy.
Final thoughts
The best gearing is highly personal. Fitness, terrain, bike type, and riding style all matter. Use the calculator above to compare options before buying drivetrain parts, and you can build a setup that feels right on every ride.