Bicycle Gear Ratio & Speed Calculator

Bicycle gear ratio describes the mechanical advantage of a specific combination of chainring (front) and sprocket (rear) teeth. It determines how far the bike travels with each complete pedal revolution and directly affects climbing ability, speed, and cadence comfort.

Gear ratio formula: Gear Ratio = Chainring Teeth / Sprocket Teeth

Development (distance per pedal revolution): Development (meters) = Gear Ratio × Wheel Circumference (m) Wheel Circumference = π × Wheel Diameter

Speed formula: Speed (km/h) = Development (m) × Cadence (RPM) × 60 / 1,000

Standard wheel sizes. Watch the units here, because circumference and diameter differ by a factor of π and mixing them up is the single easiest way to get a wildly wrong speed. The presets in the calculator use the circumference column; the custom field wants the diameter column.

A note on the 700c figures, because published charts disagree: 2.096 m is the number for a 23 mm tire, not a 25. Tires have got wider over the last decade and 25 mm is now the road default, so 2.105 m is the one to use. The difference is under half a percent, but it is the kind of error that quietly propagates when someone copies a chart from 2005.

Worked example: Road bike: 50-tooth chainring, 11-tooth sprocket (top gear), 700c × 25mm wheel, cadence 90 RPM. Gear ratio = 50 / 11 = 4.55 Development = 4.55 × 2.105 = 9.57 m per revolution Speed = 9.57 × 90 × 60 / 1,000 = 51.7 km/h

Same bike in climbing gear (34T chainring, 28T sprocket): Gear ratio = 34 / 28 = 1.21 Development = 1.21 × 2.105 = 2.56 m Speed at 70 RPM = 2.56 × 70 × 60 / 1,000 = 10.7 km/h, which is manageable on steep grades.

Cadence targets:

• Road cycling: 85–100 RPM (efficient aerobic range)
• Mountain biking: 70–90 RPM
• Beginners: 60–75 RPM (common before building cardiovascular base)

Gear inches (older imperial measure): Gear Inches = (Chainring / Sprocket) × Wheel Diameter (inches) A 100+ gear-inch ratio represents a very hard gear suitable only for downhill sprinting.