Enter the horizontal force, distance between supports, and weight per unit length into the calculator to determine the sag of a catenary curve.

Catenary Equation Formula

The following formula is used to calculate the sag of a catenary curve.

S = {w* d^2}/{8* H}

Variables:

  • S is the sag of the catenary curve (unit of length)
  • w is the weight per unit length (force per unit length)
  • d is the horizontal distance between the supports (length)
  • H is the horizontal force (force)

To calculate the sag of a catenary curve, multiply the weight per unit length by the square of the distance between supports, and then divide by eight times the horizontal force.

What is a Catenary Curve?

A catenary curve describes the shape of a flexible chain or cable that hangs between two points under its own weight and is acted upon by gravity. The curve has a specific mathematical form and is relevant in various engineering and architectural applications, such as the design of suspension bridges and overhead power lines. Understanding the sag of a catenary curve is crucial for ensuring the structural integrity and functionality of such systems.

How to Calculate Sag in a Catenary Curve?

The following steps outline how to calculate the sag in a Catenary Curve.


  1. First, determine the horizontal force (H) in the cable or chain.
  2. Next, determine the horizontal distance between the supports (d).
  3. Next, determine the weight per unit length (w) of the cable or chain.
  4. Next, gather the formula from above = S = (w * d^2) / (8 * H).
  5. Finally, calculate the sag (S) in the catenary curve.
  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.

horizontal force (H) = 500 N

distance between supports (d) = 100 m

weight per unit length (w) = 2 N/m