Enter the liquid limit, the natural moisture content, and the plasticity index into the Consistency Index Calculator. The calculator will evaluate the Consistency Index. 

Consistency Index Formula

The following formula is used to calculate the Consistency Index. 

CI = (LL - NMC) / PI


  • CI is the Consistency Index ( )
  • LL is the liquid limit 
  • NMC is the natural moisture content 
  • PI is the plasticity index 

To calculate the consistency index, subtract the natural moisture content from the liquid limit, then divide by the plasticity index.

How to Calculate Consistency Index?

The following steps outline how to calculate the Consistency Index.

  1. First, determine the liquid limit.
  2. Next, determine the natural moisture content. 
  3. Next, determine the plasticity index. 
  4. Next, gather the formula from above = CI = (LL – NMC) / PI.
  5. Finally, calculate the Consistency 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.

liquid limit = 10

natural moisture content = 5

plasticity index = 2

CI = (LL – NMC) / PI =  ?