Bicycle Gear Ratio & Speed Calculator
Calculate bicycle gear ratio, gear inches, and speed at a given cadence.
Enter chainring size, rear cog, and wheel diameter.
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 circumferences:
- 700c × 25mm road tire: 2.096 m
- 700c × 28mm road tire: 2.136 m
- 26" MTB tire (2.1"): 2.073 m
- 29" MTB tire (2.2"): 2.326 m
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 × 2.096 = 9.54 m per revolution Speed = 9.54 × 90 × 60 / 1,000 = 51.5 km/h
Same bike in climbing gear (34T chainring, 28T sprocket): Gear ratio = 34 / 28 = 1.21 Development = 1.21 × 2.096 = 2.54 m Speed at 70 RPM = 2.54 × 70 × 60 / 1,000 = 10.7 km/h — 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.