Enter the crankshaft pulley diameter (in) and the alternator pulley diameter (in) into the Calculator. The calculator will evaluate the Alternator Pulley Ratio. 

Alternator Pulley Ratio Formula



  • APR is the Alternator Pulley Ratio (in/in)
  • CPD is the crankshaft pulley diameter (in)
  • APD is the alternator pulley diameter (in)

To calculate Alternator Pulley Ratio, divide the crankshaft pulley diameter by the alternator pulley diameter.

How to Calculate Alternator Pulley Ratio?

The following steps outline how to calculate the Alternator Pulley Ratio.

  1. First, determine the crankshaft pulley diameter (in). 
  2. Next, determine the alternator pulley diameter (in). 
  3. Next, gather the formula from above = APR = CPD / APD.
  4. Finally, calculate the Alternator Pulley Ratio.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

crankshaft pulley diameter (in) = 200

alternator pulley diameter (in) = 100


What is the importance of calculating the Alternator Pulley Ratio?

The Alternator Pulley Ratio is crucial for ensuring the alternator operates efficiently. A correct ratio ensures the alternator generates enough power to charge the vehicle’s battery while avoiding excessive wear or damage.

Can a wrong Alternator Pulley Ratio affect vehicle performance?

Yes, an incorrect ratio can lead to poor battery charging, which might result in power loss for the vehicle’s electrical systems, affecting overall performance and reliability.

How often should the Alternator Pulley Ratio be checked?

It’s advisable to check the ratio whenever there are changes to the alternator or crankshaft pulley, or if there are charging issues with the vehicle. Regular maintenance checks can also include verifying this ratio.