Bicycle Drivetrain Ratio CalculatorFree online fitness & health calculator — instant results, no sign-up
Calculate gear ratio and distance traveled per crank revolution.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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About the Bicycle Drivetrain Ratio Calculator
The Bicycle Drivetrain Ratio Calculator uses chainring teeth, rear sprocket teeth, and wheel rollout circumference to calculate gear ratio and distance traveled per crank revolution. It helps you compare bicycle gearing by showing how many times the rear wheel turns and how far the bicycle moves for each full turn of the cranks.
- Chainring teeth
- The number of teeth on the selected front chainring is a unitless whole-number count, with a default of 50.
- Rear sprocket teeth
- The number of teeth on the selected rear sprocket is a unitless whole-number count, with a default of 17.
- Wheel rollout circumference (m)
- The distance the bicycle rolls during one complete wheel revolution is measured in meters, with a default of 2.1 m.
Formula and method
R = T_f / T_r; D = R × C = (T_f / T_r) × C. With the default inputs: R = 50 / 17 ≈ 2.94; D = (50 / 17) × 2.1 ≈ 6.18 m/crank revolution.
- T_fNumber of teeth on the front chainring.
- T_rNumber of teeth on the rear sprocket.
- CWheel rollout circumference in meters per wheel revolution.
- RUnitless gear ratio, representing wheel revolutions per crank revolution for a conventional chain-driven bicycle with direct rear-hub drive.
- DDevelopment: distance traveled in meters per complete crank revolution.
Divide the chainring tooth count by the rear sprocket tooth count to obtain the gear ratio. Multiply the unrounded ratio by the wheel rollout circumference to obtain development, then round the displayed results to two decimal places. Using 50 chainring teeth, 17 rear sprocket teeth, and a 2.1 m circumference gives a gear ratio of 2.94 and development of 6.18 m/crank revolution.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Chainring teeth50
- Rear sprocket teeth17
- Wheel rollout circumference2.1 m
Results
- Gear ratio2.94
- Development6.18 m/crank revolution
How to use the Bicycle Drivetrain Ratio Calculator
- 1Enter the tooth count of the front chainring you want to evaluate; the default is 50.
- 2Enter the tooth count of the selected rear sprocket; the default is 17.
- 3Enter the wheel rollout circumference in meters; the default is 2.1.
- 4Read the gear ratio and development outputs: the default inputs produce 2.94 and 6.18 m/crank revolution.
- 5Change the chainring or sprocket tooth count to compare gearing, keeping circumference unchanged when using the same wheel and tire.
Reading your result
The Gear ratio row shows how many rear-wheel revolutions correspond to one full crank revolution: 2.94 means approximately 2.94 wheel turns per crank turn. The Development row expresses that gearing as travel distance: 6.18 m/crank revolution means approximately 6.18 meters per full crank turn. With the same wheel circumference, higher values mean taller gearing and more distance per crank turn; lower values mean shorter gearing, generally making climbing easier but covering less distance per turn.
Limitations
The calculation assumes a conventional chain drivetrain with the selected rear sprocket driving the wheel directly, an engaged drivetrain, and rolling without tire slip. It does not account for additional gearing in internally geared hubs or crank gearboxes. Actual rollout varies with tire size, pressure, load, and surface conditions. Tooth counts must be positive whole numbers, and circumference must be positive. These outputs do not independently predict speed, pedaling effort, power, or drivetrain efficiency; speed also requires cadence.
Common questions
Does a gear ratio of 2.94 mean the bicycle travels 2.94 meters per crank turn?+
No. It means approximately 2.94 wheel revolutions per crank turn. Multiplying the unrounded ratio of 50/17 by the 2.1 m wheel circumference gives the development of 6.18 m/crank revolution.
How does a larger rear sprocket change the results?+
With the chainring and circumference unchanged, a larger rear sprocket lowers both gear ratio and development. The bicycle travels less distance per crank turn, and the shorter gearing generally makes climbing easier.
How should I measure wheel rollout circumference?+
Mark the tire's contact position on level ground, roll the bicycle straight forward through one complete wheel revolution, and measure the distance in meters. Use normal tire pressure and representative rider load when practical.
Can I use these results for an internally geared hub?+
Not directly unless the selected hub gear has a 1:1 internal ratio. For other hub gears, multiply the calculated gear ratio and development by the hub's wheel-revolutions-per-sprocket-revolution factor.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.