Enter the allowable stress of the material, length of the beam, depth of the beam, and moment of inertia into the calculator to determine the maximum span of a floor beam.

Floor Beam Span Formula

The following formula is used to calculate the maximum span of a floor beam.

S = (F * L^2) / (8 * D * I)

Variables:

  • S is the maximum span of the floor beam (feet)
  • F is the allowable stress of the material (psi)
  • L is the length of the beam (feet)
  • D is the depth of the beam (inches)
  • I is the moment of inertia (in^4)

To calculate the maximum span of a floor beam, multiply the allowable stress of the material by the square of the length of the beam. Divide this result by the product of 8, the depth of the beam, and the moment of inertia.

What is a Floor Beam Span?

A Floor Beam Span refers to the distance a floor beam can safely cover without support. It is a crucial aspect in construction and architecture, determining the strength and stability of a structure. The span is influenced by factors such as the type of material used, the weight the beam is expected to support, and the beam’s size. The longer the span, the stronger and larger the beam needs to be to prevent sagging or collapse.

How to Calculate Floor Beam Span?

The following steps outline how to calculate the Floor Beam Span.


  1. First, determine the allowable stress of the material (F) in psi.
  2. Next, determine the length of the beam (L) in feet.
  3. Next, determine the depth of the beam (D) in inches.
  4. Next, determine the moment of inertia (I) in in^4.
  5. Next, gather the formula from above = S = (F * L^2) / (8 * D * I).
  6. Finally, calculate the Floor Beam Span.
  7. 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.

allowable stress of the material (F) = 5000 psi

length of the beam (L) = 10 feet

depth of the beam (D) = 12 inches

moment of inertia (I) = 500 in^4