Beam Size Calculator
A beam size calculator is designed to determine the appropriate dimensions of a beam based on the load it must support and the span it covers.
Beams serve as essential structural elements, transferring loads from floors, roofs, and other components.For instance, if you are renovating a home and need to remove a load-bearing wall, you will require a beam to support the load above.
A beam size calculator will factor in:
- The span of the opening (e.g., 12 feet)
- The load the beam needs to support (e.g., roof and second floor)
- The type of material (e.g., steel, wood, or engineered lumber)
- Any deflection limits
Using these parameters, the calculator recommend a specific beam size, such as a W8x31 steel beam or a 7.25″ x 11.25″ Parallam PSL beam.
Beam Size Calculation Table
| Span (ft) | Total Load (lbs/ft) | Douglas Fir-Larch Beam Size |
|---|---|---|
| 8 | 500 | 4×8 |
| 10 | 500 | 4×10 |
| 12 | 500 | 4×12 |
| 14 | 500 | 6×10 |
| 16 | 500 | 6×12 |
| 8 | 1000 | 4×10 |
| 10 | 1000 | 4×12 |
| 12 | 1000 | 6×12 |
| 14 | 1000 | 6×14 |
| 16 | 1000 | 8×14 |
Beam Size Calculation Formula
A formula for the maximum bending moment is:
M = (w * L^2) / 8Where:
- M = Maximum bending moment (in lb-ft)
- w = Uniform load per linear foot (in lb/ft)
- L = Span length (in feet)
To calculate the maximum bending moment for a 12-foot beam supporting 500 lb/ft:
M = (500 * 12^2) / 8 = 9,000 lb-ftThis result is used to select an appropriate beam size based on the material’s strength properties.
Calculating the beam size involves complex formulas that consider bending stress, shear stress, and deflection.
What size beam for a 12 foot span?
To find the beam size for a 12-foot span supporting a typical residential load of 50 pounds per square foot (psf) with a tributary width of 10 feet, follow these steps:
Calculate the uniform load: 50 psf * 10 ft = 500 lb/ft
Calculate the maximum bending moment: M = (500 * 12^2) / 8 = 9,000 lb-ft
Convert to inch-pounds: 9,000 lb-ft * 12 in/ft = 108,000 lb-in
Assuming Douglas Fir-Larch lumber with a bending stress of 1,500 psi: Required Section Modulus = 108,000 lb-in / 1,500 psi = 72 in^3
Consulting lumber tables, a 4×12 beam has a section modulus of 78.54 in³, which exceeds the requirement.
For a 12-foot span supporting this load, a 4×12 Douglas Fir-Larch beam would be suitable.
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