Bike Gear Ratio Calculator
Calculate a bicycle gear ratio from chainring teeth and rear sprocket teeth.
Your inputs
Bike Gear Ratio Results
2 :1
Chainring teeth ÷ rear sprocket teeth
Full result table
| Crank revolutions | Ideal driven sprocket revolutions |
|---|---|
| 1 | 2 |
| 5 | 10 |
| 10 | 20 |
A gear ratio alone does not determine speed. Wheel size, cadence, drivetrain losses and conditions also matter.
Let’s work it out.
Ask about this tool, enter your values, or understand your result.
Ask in your own language.
How to use Bike Gear Ratio Calculator
- Enter chainring teeth, rear sprocket teeth.
- Calculate and compare the labelled result views. Check that every input uses the displayed unit.
- Read the worked example and limits before applying the answer.
Worked example
A 50-tooth chainring and 25-tooth sprocket give a 2:1 ratio.
Formula, accuracy & limitations
Gear ratio = chainring teeth ÷ rear sprocket teeth.
A gear ratio alone does not determine speed. Wheel size, cadence, drivetrain losses and conditions also matter.
Calculations use your inputs. Main numeric values show up to six decimal places, percentages up to two, and chart labels up to four. Time results use hours, minutes and seconds. Very small nonzero values use scientific notation.
Use tooth counts from one gear combination
Enter the chainring teeth and the selected rear sprocket teeth. The ideal driven-sprocket revolutions per crank revolution equal their ratio. Positive whole tooth counts are required; a zero sprocket cannot form a meaningful ratio.
A ratio alone is not road speed
The table compares ideal revolutions at several crank-turn counts. The rings are illustrative and do not show actual tooth geometry. Wheel circumference, cadence, freewheeling, drivetrain losses and route conditions are not supplied, so the page does not calculate speed or shifting advice.
Frequently asked questions
Does 2:1 mean the bicycle travels twice as far?
It means two ideal driven-sprocket rotations per crank revolution for that combination. Road distance also needs wheel geometry.
Are the two rings drawn to mechanical scale?
They are labelled illustrations. Use the tooth counts and table, not ring diameter, to read the ratio.
What happens if I choose a larger rear sprocket?
With the same front chainring, the front-to-rear ratio falls. The driven sprocket makes fewer revolutions per crank revolution in this ideal ratio model.
Can the ratio alone tell me speed in km/h?
No. Speed also requires cadence and wheel rollout. This page reports gearing geometry, without modelling tyre size, losses or riding conditions.
