Beam & Joist Span Lookup
Enter the span you need and a joist spacing to find the smallest listed member size that covers it, for quick reference only.
Span table
How it works
Each listed size has a maximum span for a given joist spacing. Wider spacing means each joist supports more floor or roof area (a larger tributary width), which lowers its maximum safe span. This lookup simply finds the smallest listed size whose maximum span meets or exceeds the span you need.
Worked example
For a 12 ft span at 16" on-center spacing, a 2x8 (max span 11.9 ft) falls just short, so the smallest size that covers it is a 2x10 (max span 15.2 ft).
Assumptions
- Values are illustrative reference ranges, not tied to a specific species, grade, or load combination.
- Your local building code's official span tables and load requirements always take precedence.
- Point loads, cantilevers, and non-uniform loading are not modeled.
Reference
Wood span table methodology: American Wood Council.
Related tools
Frequently asked questions
Are these beam span values code-accurate for my location?
No — they're illustrative reference ranges. Confirm with your local building code span tables and a structural engineer.
Why does joist spacing matter for span?
Wider spacing means each joist carries more tributary load, which reduces its maximum safe span.
What should I do if my span exceeds every listed size?
Consider a larger or engineered member, an intermediate support, or closer spacing, and confirm with a structural engineer.