Enter the plastic limit and the liquid limit into the Plasticity Index Calculator. The calculator will evaluate the Plasticity Index. 

Plasticity Index Formula

The following two example problems outline the steps and information needed to calculate the Plasticity Index.

PI = PL – LL


  • PI is the Plasticity Index ( )
  • PL is the plastic limit 
  • LL is the liquid limit 

How to Calculate Plasticity Index?

The following steps outline how to calculate the Plasticity Index.

  1. First, determine the plastic limit. 
  2. Next, determine the liquid limit. 
  3. Next, gather the formula from above = PI = PL – LL.
  4. Finally, calculate the Plasticity Index.
  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.

plastic limit = 6

liquid limit = 4

PI = PL – LL = ?