Understanding Beam Spans
The span of a beam is the distance it can safely cover without support. This calculator determines the maximum span for a built-up wood beam, which consists of multiple pieces of dimensional lumber fastened together. The span depends on the wood species, beam size (like 2x10), number of plies, and the tributary width (the floor area the beam supports).
Our calculations are based on standard engineering principles and common building codes (40 PSF live load, 10 PSF dead load, L/360 deflection limit). However, they are for planning purposes only.
Species & Size Comparison
| Factor | Impact on Span | Example |
|---|---|---|
| Wood Species | Stronger species like Southern Pine allow for longer spans than Douglas Fir. | A Pine beam can span further than a Fir beam of the same size. |
| Beam Height | A taller beam (e.g., 2x12) is significantly stronger and can span much further than a shorter one (e.g., 2x8). | Increasing size from 2x10 to 2x12 can add several feet to the max span. |
| Number of Plies | Adding plies increases the beam's width and strength, allowing for longer spans. | A 3-ply beam is much stronger than a 2-ply beam. |
| Tributary Width | A larger tributary width means the beam supports more weight, which reduces the maximum allowable span. | A beam supporting a 16-foot width can span less than half the distance of one supporting a 4-foot width. |
How to Use the Calculator
- Select the wood species for your beam.
- Choose the nominal size of the lumber (e.g., 2x10).
- Select the number of plies (individual boards) that will be fastened together to create the beam.
- Choose the tributary width—the width of the floor area the beam is responsible for supporting.
- Click "Calculate Span" to see the maximum recommended distance the beam can cover.
Chart: Span vs. Number of Plies
This chart visualizes how adding plies increases the maximum span for the selected beam configuration.
Frequently Asked Questions
What does "tributary width" mean?
Tributary width is half the distance to the next support on one side of the beam plus half the distance to the next support on the other side. It represents the total width of the floor area that the beam must support.
Can I use this for exterior decks or roof beams?
No. This calculator is designed for interior floor beams under specific load conditions. Decks and roofs have different load requirements (like snow loads) and require separate calculations. Always consult a qualified engineer for your specific project.