Microlam Beam Size Calculator
Check an LVL or Microllam beam for span load, bending stress, shear, live and total deflection, bearing pressure, and the smallest depth that passes the selected limits.
Beam check results
| LVL grade | E value | Fb bending | Typical Fv |
|---|---|---|---|
| 2.0E LVL | 2,000,000 psi | 2,600 psi | 285 psi |
| 1.9E LVL | 1,900,000 psi | 2,600 psi | 285 psi |
| 1.8E LVL | 1,800,000 psi | 2,400 psi | 285 psi |
| 1.7E LVL | 1,700,000 psi | 2,300 psi | 250 psi |
| 1.5E LVL | 1,500,000 psi | 2,200 psi | 250 psi |
| Depth | 2-ply width | Section modulus | Moment inertia |
|---|---|---|---|
| 7.25 in | 3.50 in | 30.7 in³ | 111 in⁴ |
| 9.50 in | 3.50 in | 52.6 in³ | 250 in⁴ |
| 11.875 in | 3.50 in | 82.2 in³ | 488 in⁴ |
| 14.00 in | 3.50 in | 114.3 in³ | 800 in⁴ |
| 16.00 in | 3.50 in | 149.3 in³ | 1,195 in⁴ |
| Use case | Live load | Dead load | Common limit |
|---|---|---|---|
| Residential floor | 40 psf | 10 to 15 psf | L/360 live |
| Sleeping room | 30 psf | 10 psf | L/360 live |
| Deck joists to beam | 40 psf | 10 psf | L/360 live |
| Roof with snow | 20 to 50 psf | 10 psf | L/240 snow |
| Garage header | 20 psf roof | 15 psf | L/240 total |
| Bearing length | 2-ply area | 3-ply area | Use note |
|---|---|---|---|
| 1.50 in | 5.25 in² | 7.88 in² | Minimum framing seat |
| 3.00 in | 10.50 in² | 15.75 in² | Common wood support |
| 3.50 in | 12.25 in² | 18.38 in² | Full 2x4 post face |
| 5.50 in | 19.25 in² | 28.88 in² | Wider post or pocket |
The idea starts out on the blueprint, open-concept living room, but when it comes time to do the math in the field, it’s got to be done with care. Remove this wall, you think; let light pour through here.
Only there’s no ordinary piece of wood supporting the second floor; those is engineered laminated veneer lumber, known as microlam. And they don’t take kindly to getting the size wrong. Getting the size wrong doesn’t just mean a sagging ceiling. Getting the size wrong doesn’t just mean a sagging ceiling; it means expensive remediation or worse.
How to Calculate the Right Beam Size
That’s where the calculator above comes in: Plug in your span and load estimates, and it’ll tell you the recommended depth of the beam. The question is: how do you know if the input represent anything real-world?
The first things to consider are the tributary width and the span. What is the span? It’s the obvious gap between whatever posts or bearing walls is holding up the roof or floor. What is the tributary width? It’s the amount of roof or floor that sends weight down into that particular beam.
Say the beam runs down the middle of the room, which is twenty-four feet long. Then each side adds there weight to the beam. There are twelve feet on either side.
That’s the portion of the problem folks fail to understand. They look at a large space and imagine this beam must bear the entire load, or they fail to consider the weight of building itself, which is the dead load. First you calculate the weight of insulation, drywall, subfloor, joists, then think about the weight of sofas and human bodies strolling back and forth.
Deflection limits satisfy both building codes and comfort requirements. An L/360 limit (the beam must not deflect more than the span divided by 360) is typical for most residential floors, which see a lot of live load, while roof beams are frequently allowed a more relaxed L/240 due to less frequent loads. This ensures that the floor do not become bouncy, causing cracks in the walls.
The calculator takes care of the complicated math for shear and bending stress as well as testing the modulus of elasticity against the chosen grade of materials. It shows you whether you can make do with an 11.875-inch beam or whether you’ll have to go up to fourteen inches.
But it will also check bearing pressure. Bearing pressure is the concentrated force of the beam pushing down onto the supports at each end. Another small detail, but it matters: Don’t have your bearing too short, because then you risk crushing the wood (or masonry) below with the beam. For wood posts, we typically use a three-inch bearing length. I’ve had this problem before where the post sits on a narrow ledger, so you want some extra surface area to spread out that load.
The quality of the material itself vary depending on the manufacturer. For example, a 1.5E grade is not as stiff (deflects more) as a 2.0E LVL. So it’s important to note which brand you are looking at, since their values will be different from each other. Look at the chart on the page; It shows how different grades impact the E value and allowed stress values. Just because one brand says it’s 2.0E doesn’t mean another brand is. That’s what the stamp on the board indicates. That matters most about that piece of wood.
Going cheap up front by using the conservative values on a lesser grade may cost you down the road when your beam fail the deflection test.
There is another wrinkle called point loads. By “point load,” I mean something like a heavy chandelier, or the concentrated load of a post sitting somewhere in the middle of your span. This kind of load spikes the stress in the very center of the span, which isn’t captured with uniform loading. The tool lets you add a center point load to reflect this reality. Here it’s better to err on the side of caution. Two inches of extra depth won’t break the bank; repairing cracks in your ceiling or having to replace a failed support will.
Your goal is to find the minimal depth that meets all the tests while not wasting any headroom or materials. Then again, once you get your results: don’t stop there. Look at the usage ratios (Bending & Shear). Is one at 40% and another at 95%? Good! You’re being efficient, but you’ve got no margin for error. Both are hovering around 100%? You’re walking a tightrope.
Margins mean safety. Construction margins are buffers for the unforeseen weight of an upcoming renovation or the small variance in the quality of the materials used. The calculator presents you with the engineering baseline. Now, all that’s left for you is to add common sense and any applicable local code requirements. Always have a qualified pro sign-off on the final design.
But knowing these inputs will help you estimate and plan. You’ll start speaking the language of the builder. You’ll understand why the beam is that deep and why it’s sitting right where it is. It is more than just wood. It’s a calculated solution to a heavy problem. And when those lights come on in that open room, you’ll know exactly what is holding it up.
