Enter the focal length (mm) and the crop factor into the Calculator. The calculator will evaluate the Effective Focal Length. 

Effective Focal Length Formula



  • EFL is the Effective Focal Length (mm)
  • FL is the focal length (mm)
  • CF is the crop factor

To calculate Effective Focal Length, multiply the focal length by the crop factor.

How to Calculate Effective Focal Length?

The following steps outline how to calculate the Effective Focal Length.

  1. First, determine the focal length (mm). 
  2. Next, determine the crop factor. 
  3. Next, gather the formula from above = EFL = FL * CF.
  4. Finally, calculate the Effective Focal Length.
  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.

focal length (mm) = 50

crop factor = 1.25