Beam Span Calculator
Estimate the maximum allowable span for floor joists based on lumber species, grade, size, spacing, and load.
Provisional — do not use for construction
The span values behind this calculator have not been verified against the printed IRC Table R502.3.1(1)/(2). Grades other than No. 2 are scaled by an approximate factor rather than read from the table, and the Southern Pine values predate the 2013 SPIB design-value revision. Confirm every span against the adopted code edition or a design professional before relying on it.
Select the lumber species for your beam or joist
Structural grade of the lumber
Nominal depth and width of the member
Center-to-center spacing of joists or beams
Structure and material weight
Occupancy and environmental loads
Results
Maximum Allowable Span
12'-0"
feet-inches
Section Modulus
13.14
in³
Deflection Criteria (L/360)
Allowable deflection 0.40" at this span
Table span is governed by L/360 live-load deflection (IRC R301.7). Allowable deflection at this span is shown above.
Code Reference
IRC Table R502.3.1(1) / IBC Table 2308.8 – Floor joist and beam spans based on species, grade, size, spacing, and loads. Values shown for 40 psf live load with grade adjustments applied.
Disclaimer: This calculator is for reference only. Always verify with your local building department and consult IRC/IBC tables for your specific jurisdiction and load conditions.