Beam Calculator
Enter your span and load per foot for a starting beam size. This is a rough estimate, not a structural spec.
What your result means
The recommended size is a rough starting point only, based on the span. Real beam sizing depends on the wood species, the load combination, and deflection limits, none of which this captures. For anything load-bearing, size the beam against span tables and have a licensed structural engineer confirm it. Spans over 12 ft usually need an engineered LVL or PSL beam.
How to use this calculator
- Measure or specify the beam span in feet.
- Standard residential load: 40 lbs/ft. Higher for snow areas or heavy loads.
- Read total load and recommended beam size.
- CRITICAL: This is a simplified estimate. Consult a structural engineer for load-bearing applications.
- LVL or engineered beams required for spans over 12 ft.
The formula
Total load is the span times the load per foot. The size is a simplified lookup against the span. It does not account for species, deflection, or load combinations, which is why it's a starting point, not a spec.
Worked example
Say you've got a 10 ft span carrying 40 lbs a foot. That's a 400 lb total load, and the rough starting size is a doubled 2x10. Before you build, confirm that against span tables and an engineer.
Simplified beam size by span (verify with an engineer)
| Span | Starting size |
|---|---|
| Up to 6 ft | 2x6 doubled |
| Up to 8 ft | 2x8 doubled |
| Up to 10 ft | 2x10 doubled |
| Up to 12 ft | 2x12 doubled |
| Over 12 ft | LVL / engineered |
Tips & gotchas
- This is simplified. Real beam sizing needs the modulus, the moment of inertia, and load combinations.
- Spans over 12 ft usually need an LVL or PSL engineered beam.
- Always have a licensed structural engineer review a load-bearing beam.
- Doubled 2x lumber is common, like two 2x10s nailed together.
- Check local code for the required beam size at your span.
Frequently asked questions
What size beam for a 10 ft span?
Typically a doubled 2x10, but always confirm against span tables or an engineer.
Can I use this for load-bearing walls?
As a rough estimate only. Consult a structural engineer for anything load-bearing.
What is an LVL beam?
Laminated Veneer Lumber, an engineered beam stronger than solid lumber.
How much does an LVL beam cost?
$5 to $15 a linear foot depending on the size.
When do I need an engineered beam?
Spans over 12 ft, heavy point loads, or wherever code requires it.
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Estimates only — see our full disclaimer.