Select the sprocket speed ratio or tooth count to solve for, then enter the two requested values.
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Sprocket Ratio Formula
This calculator defines sprocket speed ratio as driving teeth divided by driven teeth, equal to driven speed divided by driving speed. The reduction ratio is its reciprocal. Inverse tooth counts are theoretical; real sprockets require whole teeth.
- SR = sprocket ratio
- T_d = teeth in the driving sprocket
- T_D = teeth in the driven sprocket
If you know the sprocket ratio and the driven sprocket teeth, the driving sprocket teeth can be found with:
If you know the driving sprocket teeth and the sprocket ratio, the driven sprocket teeth can be found with:
- Calculate sprocket ratio: enter the teeth in the driving sprocket and driven sprocket. The calculator divides driving teeth by driven teeth.
- Calculate driving sprocket teeth: enter the sprocket ratio and driven sprocket teeth. The calculator multiplies those values.
- Calculate driven sprocket teeth: enter the driving sprocket teeth and sprocket ratio. The calculator divides the driving teeth by the ratio.
Common Sprocket Ratio Results
The table below shows how to read the result using this calculator’s definition: driving sprocket teeth divided by driven sprocket teeth.
| Driving Teeth | Driven Teeth | Sprocket Ratio | General Effect |
|---|---|---|---|
| 12 | 36 | 0.3333 | Driven sprocket turns slower with more torque |
| 15 | 30 | 0.5000 | Driven sprocket turns at half the driving speed |
| 20 | 20 | 1.0000 | Same rotational speed |
| 36 | 18 | 2.0000 | Driven sprocket turns faster with less torque |
Example Calculations
Example 1: Calculate sprocket ratio
You have a 14-tooth driving sprocket and a 42-tooth driven sprocket.
The sprocket ratio is 0.3333.
Example 2: Calculate driven sprocket teeth
You know the driving sprocket has 18 teeth and the sprocket ratio is 0.6000.
The driven sprocket should have 30 teeth.
FAQ
What is the driving sprocket?
The driving sprocket is the sprocket that supplies power to the chain. It is usually connected to the motor, engine, crank, or input shaft.
What is the driven sprocket?
The driven sprocket is the sprocket that receives power from the chain. It is usually connected to the wheel, axle, output shaft, or driven machine part.
What does a sprocket ratio less than 1 mean?
Using this calculator’s formula, a ratio less than 1 means the driving sprocket has fewer teeth than the driven sprocket. The driven sprocket will turn slower than the driving sprocket, but it will generally produce more torque.
