Enter the weight per unit length (lb/in), the length of the span (in), and the total tension (lb) into the Chain Sag Calculator. The calculator will evaluate the Chain Sag. 

Chain Sag Formula

The following formula is used to calculate the Chain Sag. 

S = w*l^2 / (8*T)


  • S is the Chain Sag (in)
  • w is the weight per unit length (lb/in) 
  • l is the length of the span (in) 
  • T is the total tension (lb) 

To calculate the chain sag, square the length of the span, multiply by the weight per unit length, then divide by the product of 8 times the total tension.

How to Calculate Chain Sag?

The following steps outline how to calculate the Chain Sag.

  1. First, determine the weight per unit length (lb/in).
  2. Next, determine the length of the span (in). 
  3. Next, determine the total tension (lb). 
  4. Next, gather the formula from above = S = w*l^2 / (8*T).
  5. Finally, calculate the Chain Sag.
  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.

weight per unit length (lb/in) = 40

length of the span (in) = 5

total tension (lb) = 30

S = w*l^2 / (8*T) =  ?