Beam Load Calculator
Calculate total beam load, required section modulus, and recommended beam size for your structural project. See also our Beam Deflection Calculator, Floor Joist Calculator, and Framing Calculator.
Load Parameters
How to Use the Beam Load Calculator
Enter the beam span (distance between supports), tributary width (the floor or roof area the beam supports on each side), dead load (weight of structure, typically 10-20 PSF for wood framing), and live load (occupancy load, 40 PSF for residential floors per IBC). Select the beam material type to determine the allowable bending stress. The calculator determines the total load, maximum bending moment, shear force, required section modulus, and suggests an appropriate beam size.
Formula
Uniform Load (PLF) = (Dead Load + Live Load) × Tributary Width
Total Load (lbs) = Uniform Load × Span
Max Moment = wL² / 8 (ft-lbs)
Max Shear = wL / 2 (lbs)
Required Section Modulus = M × 12 / Fb (in³)
Example Calculation
Span = 14 ft, Tributary Width = 12 ft
Dead Load = 15 PSF, Live Load = 40 PSF
Uniform Load = (15 + 40) × 12 = 660 PLF
Total Load = 660 × 14 = 9,240 lbs
Max Moment = 660 × 14² / 8 = 16,170 ft-lbs
Max Shear = 660 × 14 / 2 = 4,620 lbs
Req'd S (Douglas Fir, Fb=1000) = 16,170 × 12 / 1000 = 194 in³
→ Use 6×14 or engineered beam
Reference Table — Beam Capacities
| Beam Size | Section Modulus (in³) | Max Span @ 500 PLF | Weight (PLF) |
|---|---|---|---|
| 2×10 (doubled) | 21.4 | 8 ft | 5.0 |
| 2×12 (doubled) | 31.6 | 10 ft | 6.0 |
| 4×10 | 23.1 | 9 ft | 5.4 |
| 4×12 | 32.0 | 10 ft | 6.7 |
| 6×10 | 37.8 | 11 ft | 8.4 |
| 6×12 | 52.7 | 13 ft | 10.5 |
| LVL 3.5×9.5 | 52.7 | 14 ft | 7.5 |
| LVL 3.5×11.875 | 82.3 | 17 ft | 9.4 |
| W8×18 (steel) | 15.2 | 20 ft | 18.0 |
| W10×22 (steel) | 23.2 | 24 ft | 22.0 |
Frequently Asked Questions
What is tributary width?
Tributary width is the total floor or roof area that loads onto the beam, measured perpendicular to the beam. For a beam centered between two parallel walls 24 feet apart, the tributary width is 12 feet (half the distance to each adjacent support).
What live load should I use for residential floors?
The IBC requires 40 PSF for habitable rooms, 30 PSF for sleeping rooms, and 100 PSF for decks and balconies. Garages require 50 PSF minimum. Always check your local building code as requirements may vary.
What is the difference between LVL and solid wood beams?
LVL (Laminated Veneer Lumber) has an allowable bending stress of 2,600 psi compared to 1,000 psi for Douglas Fir #2. This means LVL beams can span further or carry more load in the same size. LVL is also more dimensionally stable and available in longer lengths.
How do I determine dead load?
Dead load includes the weight of all permanent construction: framing (3-5 PSF), subfloor (2-3 PSF), finished floor (1-5 PSF), ceiling below (2-5 PSF), and mechanical/electrical (1-2 PSF). A typical wood-framed floor totals 10-15 PSF dead load.
When should I use a steel beam instead of wood?
Steel beams are preferred for spans over 20 feet, heavy point loads, limited depth conditions (steel is stronger per inch of depth), and where fire resistance is needed. Steel W-shapes are also ideal for open floor plans where columns must be minimized.
Do I need an engineer for beam sizing?
Most building departments require engineered calculations for structural beams, especially for load-bearing walls, headers over 6 feet, and any beam supporting more than one floor. This calculator provides preliminary sizing — always have a licensed structural engineer verify critical members.