Wood Beam Calculator
Find the right wood beam size for your span and load. Compare SPF lumber and LVL options with deflection checks for floors, decks, and roofs.
All Beam Options for 12' Span
| Beam Size | Width | Depth | Max Span | Species | Status |
|---|---|---|---|---|---|
| 2×12 | 1.5" | 11.25" | 13' | SPF | Recommended |
| 2-ply 2×10 | 3" | 9.25" | 13' | SPF | OK |
| 2-ply 2×12 | 3" | 11.25" | 16' | SPF | OK |
| 3-ply 2×10 | 4.5" | 9.25" | 16' | SPF | OK |
| 3-ply 2×12 | 4.5" | 11.25" | 19' | SPF | OK |
| 3.5×9.25 LVL | 3.5" | 9.25" | 16' | LVL | OK |
| 3.5×11.25 LVL | 3.5" | 11.25" | 20' | LVL | OK |
| 3.5×14 LVL | 3.5" | 14" | 24' | LVL | OK |
How It Works
Enter your beam span (the unsupported distance between posts or walls), tributary width (half the joist span on each side), and the dead and live loads in pounds per square foot (psf).
The calculator computes total load and finds the minimum beam size from standard SPF lumber and LVL options. It shows deflection limits at L/360 (floors) and L/240 (roofs/decks) so you can verify compliance.
The results table shows all beam options that work for your span, with the recommended (smallest sufficient) beam highlighted. Always consult a structural engineer for load-bearing beams.
Frequently Asked Questions
How do I determine what size beam I need?
Calculate total load: (dead load + live load) x tributary width x span. Dead load is typically 10 psf for residential floors; live load is 40 psf for floors per IRC code. Then find the smallest beam from span tables that can carry your span. This calculator does this automatically.
What is tributary width?
Tributary width is the distance from the beam to the midpoint of the next support on each side. If joists span 16 feet between a beam and a wall, the tributary width is 8 feet (half the joist span). For beams supporting joists from both sides, add both half-spans.
When should I use LVL instead of dimensional lumber?
Laminated veneer lumber (LVL) is stronger and more dimensionally stable than solid lumber. Use LVL for spans over 16 feet, heavy loads, or where you need a narrower beam profile. LVL is also better for long-term deflection resistance and does not crown, twist, or bow like solid lumber.
What do L/360 and L/240 deflection limits mean?
L/360 means the beam can deflect no more than 1/360th of its span length — for a 12-foot span, that is 0.4 inches. L/360 is the standard for floors and plaster ceilings. L/240 is less strict and used for roofs and exterior decks. These limits prevent cracking, bouncy floors, and visible sag.