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Span Tables Calculator

Look up allowable spans for floor joists, ceiling joists, and rafters per IRC/IBC prescriptive tables.

Half span each side of beam

Results

Floor Joist Span Table (SPF #2, L/360)

40 psf live load + 10 psf dead load

Joist Size 12" o.c. 16" o.c. 19.2" o.c. 24" o.c.
2×6 9'-11" 9'-0" 8'-4" 7'-7"
2×8 13'-1" 11'-10" 11'-0" 10'-0"
2×10 16'-5" 14'-11" 13'-9" 12'-4"
2×12 18'-8" 17'-0" 15'-9" 14'-4"

Important Notes

  • Values are based on IRC 2021 prescriptive tables
  • Spans are clear span between supports
  • Deflection limit: L/360 for floors, L/240 for roofs
  • Verify lumber grade marking matches specification
  • Always consult local building codes for final design
  • Engineered lumber (LVL, I-joists) may allow longer spans