Bike gear calculator
Enter your chainring, cog and wheel, get gear inches and your speed at a cadence.
Separate the sizes with commas, up to 4 chainrings and 16 cogs.
Used for the gain ratio only. Clear the field to skip it.
How do you calculate gear ratio and gear inches?
The gear ratio is the chainring teeth divided by the cog teeth: 50 ÷ 17 = 2.94. Sheldon Brown defines gear inches as the diameter of the drive wheel times the front sprocket divided by the rear sprocket. On a 700 × 23 wheel, whose rolling diameter is about 26.3 inches, a 50/17 gear is about 77.3 gear inches. Brown notes that the lowest gear on most mountain bikes is around 22 to 26 gear inches and the highest on road racing bikes usually around 108 to 110.
What are meters of development?
Development, also called rollout, is the distance the bicycle travels for one turn of the cranks, usually in meters. It is the gear ratio times the wheel circumference: 2.94 × 2.097 m = 6.17 m for a 50/17 gear on a 700 × 23 wheel (2,097 mm round).
How do I find my speed from cadence?
Multiply the development by the cadence in rpm to get meters per minute, then multiply by 60 for meters per hour. At 90 rpm in 50/17 on a 700 × 23 wheel: 6.17 m × 90 × 60 = 33.3 km/h, or 20.7 mph. To find the cadence for a target speed, divide the speed by the development and by 60.
What wheel circumference should I use?
The presets are the circumferences in Sheldon Brown's cyclecomputer calibration chart, which he says are generally accurate to within one or two percent. The real value depends on tire tread, pressure and rider weight, so a roll-out test with the rider aboard is more accurate. A rough value from the ISO size is (bead seat diameter + 2 × tire width) × π: 2,130 mm for a 28-622 tire, against 2,136 mm in the chart, and Brown adds that a road tire's actual rolling diameter is about 1% smaller.
What is a gain ratio?
Sheldon Brown's gain ratio also counts the crank length: the wheel radius divided by the crank length, times the gear ratio. It tells how far the bicycle moves for each unit the pedal travels in its circle. His example: a 680 mm road wheel (340 mm radius) with 170 mm cranks and a 53/19 gear gives 2.0 × 53 ÷ 19 = 5.58.
Turn a speed into a running pace with the pace calculator. The same gear idea for cars is in the RPM to MPH calculator.
Sources: Sheldon Brown, Bicycle Glossary (“Gear Inches” and “Development”), “Gain Ratios — A New Way to Designate Bicycle Gears” and “Cyclecomputer/GPS Calibration” with Sheldon Brown’s Cyclecomputer Calibration Chart (sheldonbrown.com). How we check our calculators.