LVL beam size is the shallowest depth whose bending, shear and sag all pass: a 12 ft floor beam with a 10 ft tributary width at 40 psf live and 10 psf dead load needs a 2-ply 1¾ x 9½ in LVL. Enter your span and load above and the calculator sizes 1, 2, 3 and 4 plies of 2.0E Microllam LVL, with the beam's own weight included.
How the LVL beam size is found
The calculator treats the beam as a simple span with a uniform load, and checks four things for every depth from 5½ to 20 in:
- Bending: the moment w × L² ÷ 8 must not exceed the allowable moment of the section.
- Shear: the end reaction w × L ÷ 2 must not exceed the allowable shear.
- Live load sag: at most span ÷ 360 (or ÷ 480 if you pick the stricter limit).
- Total load sag: at most span ÷ 240.
Load on the beam = (live psf + dead psf) × tributary width + beam weight. Sag = 5 × w × L⁴ ÷ (384 × E × I), with E = 2,000,000 psi for 2.0E LVL.
The allowable moment and shear per 1¾ in ply come straight from the manufacturer's table, which already applies the 2,600 psi bending value, the size factor for depths other than 12 in and the 285 psi shear value. They are multiplied by the number of plies and by the load duration factor: 1.00 for a floor, 1.15 for a roof in a snow load area and 1.25 for other roofs. Sag is not adjusted for duration.
Worked example: a 12 ft floor beam
Span 12 ft, tributary width 10 ft, live load 40 psf, dead load 10 psf, floor. The line load is 10 ft × 50 psf = 500 plf, plus 9.6 plf for a 2-ply 9½ in beam, 509.6 plf.
- Bending: 509.6 × 12² ÷ 8 = 9,173 lb-ft against 2 × 5,885 = 11,770 lb-ft allowed, 78 percent.
- Shear: 3,058 lb against 2 × 3,160 = 6,320 lb allowed.
- Live sag: 0.37 in against a 0.40 in limit (144 in ÷ 360).
- Total sag: 0.48 in against a 0.60 in limit (144 in ÷ 240).
A 2-ply 9½ in beam passes; a 2-ply 9¼ in does not (its live sag is over the limit). With other ply counts the answers are 14 in for one ply, 9¼ in for three plies and 9¼ in for four plies. The least material is the 2-ply 9½ in.
LVL size chart: one 1¾ in ply of 2.0E Microllam
Allowable values per ply at 100 percent load duration, from Weyerhaeuser's Beam, Header and Column Specifier's Guide TJ-9000 (2015).
| Depth, in | Allowable moment, lb-ft | Allowable shear, lb | Moment of inertia, in⁴ | Weight, lb/ft |
|---|---|---|---|---|
| 5½ | 2,125 | 1,830 | 24 | 2.8 |
| 7¼ | 3,555 | 2,410 | 56 | 3.7 |
| 9¼ | 5,600 | 3,075 | 115 | 4.7 |
| 9½ | 5,885 | 3,160 | 125 | 4.8 |
| 11¼ | 8,070 | 3,740 | 208 | 5.7 |
| 11⅞ | 8,925 | 3,950 | 244 | 6.1 |
| 14 | 12,130 | 4,655 | 400 | 7.1 |
| 16 | 15,555 | 5,320 | 597 | 8.2 |
| 18 | 19,375 | 5,985 | 851 | 9.2 |
| 20 | 23,580 | 6,650 | 1,167 | 10.2 |
How many plies
Each ply is 1¾ in wide. Two plies make a 3½ in beam that sits flush in a 2x4 wall, three plies make 5¼ in and four plies 7 in. More plies buy stiffness and strength at the same depth, but the plies have to be fastened together as the manufacturer specifies, and side-loaded beams need their own connection design. The calculator assumes the plies share the load equally.
LVL versus sawn lumber
A 2-ply 9½ in LVL carries the load above in a beam 3½ in wide and 9½ in deep, a size that fits inside a 2x4 wall and a 2x10 floor. Sawn lumber girders are limited to the IRC tables and to the grades and sizes in them, while LVL is made in long, straight, consistent pieces to 20 in deep, which is why it is the usual answer for floor girders and for openings wider than a sawn header allows. To compare a sawn girder or header for the same job, use the beam span calculator.
Next questions
- Sag alone, for your own section: the beam deflection calculator.
- Steel instead of LVL: the steel beam calculator.
- The joists that land on the beam: the floor joist span calculator and, outdoors, the deck joist span calculator.
- A garage door or wide opening in a bearing wall: the header span calculator.
- More span and beam tools: framing and lumber calculators.
LVL sizes here come from one manufacturer's published properties for 2.0E Microllam; other brands and grades have their own tables. Bearing length, lateral bracing, holes and notches, point loads away from the center, and the posts and footings under the beam are not checked. Have an engineer or the LVL maker verify the beam before you order it.