Enter the plastic limit, the natural water content, and the plasticity index into the Liquidity Index Calculator. The calculator will evaluate the Liquidity Index. 

Liquidity Index Formula

The following formula is used to calculate the Liquidity Index. 

LI = (PL - NWC) / PI


  • LI is the Liquidity Index ( )
  • PL is the plastic limit 
  • NWC is the natural water content 
  • PI is the plasticity index 

To calculate the liquidity index, subtract the natural water content from the plastic limit, then divide by the plasticity index.

How to Calculate Liquidity Index?

The following steps outline how to calculate the Liquidity Index.

  1. First, determine the plastic limit.
  2. Next, determine the natural water content. 
  3. Next, determine the plasticity index. 
  4. Next, gather the formula from above = LI = (PL – NWC) / PI.
  5. Finally, calculate the Liquidity Index.
  6. 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 = 50

natural water content = 40

plasticity index = 2.5LI = (PL – NWC) / PI =  ?