Wood Beam Span Calculator
Find a simplified maximum allowable span for a standard dimensional lumber joist based on its size and on-center spacing.
About the Wood Beam Span Calculator
This calculator looks up a simplified maximum span for common dimensional lumber sizes used as floor joists, based on typical #2 grade Spruce-Pine-Fir span tables under a standard residential live load. It's meant as a quick reference, not a code-compliant design value.
Formula: This is a lookup table (not a single formula) based on published span tables, cross-referenced by nominal lumber size and on-center spacing.
Actual allowable spans depend on species, grade, load conditions and local building code — always confirm final joist sizing against your jurisdiction's official span tables or an engineer's stamped design before framing.