Cycling Gear Ratio Calculator

How Cycling Gear Ratio Is Calculated

Gear ratio determines how far your bike travels with each pedal revolution. It’s the fundamental relationship between chainring teeth and sprocket teeth.

Gear Ratio Formula: Gear Ratio = Chainring Teeth / Sprocket Teeth

Development (Distance Per Pedal Revolution): Development (m) = Gear Ratio × Wheel Circumference

For a 700c wheel, circumference ≈ 2.10 m with a 25mm tyre, which is the figure the wheel selector uses.

Worked Example: A road bike with a 50-tooth chainring and 12-tooth sprocket:

• Gear Ratio = 50 / 12 = 4.17
• Development = 4.17 × 2.10 = 8.75 meters per pedal stroke

At 90 RPM cadence: 8.75 × 90 × 60 = 47,250 m/hr = 47.3 km/h

Common Gear Ratio Reference:

• 34/34 (1:1), steep mountain climbing
• 39/25 (1.56:1), moderate climbing
• 50/17 (2.94:1), all-day cruising
• 53/11 (4.82:1), sprinting and descending

Optimal Cadence by Discipline:

• Road cycling: 85–100 RPM
• Mountain biking: 70–90 RPM
• Track sprinting: 110–130 RPM

Chainline Note: Avoid extreme cross-chaining, meaning big chainring with big sprocket or small with small. It wastes energy and accelerates chain wear. Most efficient gear pairs keep the chain nearly straight.

Gear inches, and why the ratio alone is not enough Gear Inches = (Chainring / Sprocket) × Wheel Diameter (inches) A 700c wheel is roughly 26.5 inches in diameter, a 26-inch mountain bike wheel about 26, and a 29er about 29. That is the point: the same 2.0 ratio is a bigger gear on a 29er than on a 26-inch wheel, so gear inches is the only figure that compares fairly across bikes. This calculator judges how hard a gear is by gear inches for exactly that reason. Under 40 is climbing territory, 65 to 90 is fast cruising, and over 90 is a sprinting gear. Track cyclists talk almost exclusively in gear inches.