Compare bicycle gearing by entering chainring teeth, sprocket teeth, wheel circumference, and cadence. See gear ratio, rollout per crank revolution, and road speed in km/h or mph.
Turn bicycle gearing and cadence into rollout and road speed
The calculator combines chainring teeth, rear-cog teeth, measured wheel circumference, and cadence. It reports the mechanical ratio, distance travelled per crank revolution, and ideal road speed without treating that speed as a performance prediction.
Use the wheel that is actually on the bike
Gear ratio equals chainring teeth divided by rear-cog teeth. Rollout, also called development, equals that ratio multiplied by wheel circumference. Because tire model, width, pressure, rim, and rider load can change effective circumference, a measured loaded rollout is more useful than a nominal wheel label.
Measure one complete wheel revolution on the ground and enter the result in millimeters or inches. The global unit setting converts the same physical circumference; it should not change gear ratio, development, or the underlying speed.
Count the teeth on the selected front ring and rear cog.
Use a positive measured wheel circumference.
Enter cadence in crank revolutions per minute.
Follow the speed equation
Ideal distance per minute equals rollout multiplied by cadence. Multiplying by 60 and converting meters to kilometers gives road speed in km/h; the imperial display converts that same speed to mph.
For example, a 50-tooth chainring, 17-tooth cog, 2.10 m circumference, and 90 rpm produce a 2.94 ratio, about 6.18 m per crank revolution, and about 33.4 km/h. The example demonstrates gearing arithmetic, not the power required to hold that cadence outdoors.
Keep mechanical speed separate from ride performance
The result assumes the selected cadence and direct wheel travel with no tire slip. It does not account for gradient, wind, drafting, surface, cornering, coasting, drivetrain flex, or whether the rider can produce the required torque and power.
Use the calculator to compare adjacent gears, estimate trainer setup, or check cadence-speed combinations. Use power, aerodynamic, and course information separately before turning one combination into a race target.
Frequently asked questions
What is bicycle gear ratio?
It is chainring teeth divided by rear-cog teeth. A 50-tooth ring with a 25-tooth cog has a ratio of 2.0, so the rear wheel turns twice per crank revolution in an ideal direct-drive calculation.
Why should I measure wheel circumference?
Nominal tire labels do not capture every rim, tire, pressure, and load combination. Because circumference is multiplied into rollout and speed, a measured value gives the more relevant scenario.
Does the calculated speed include hills or wind?
No. It is ideal mechanical road speed at the entered cadence. Gradient, wind, surface, aerodynamics, and available rider power are outside this calculation.