DeckFrame · Deck joist span calculator

Deck joist span chart — 2021 IRC R507 method

Allowable deck joist spans for No.2 grade Southern Pine, Spruce-Pine-Fir, Douglas Fir-Larch, and Hem-Fir at 12", 16", and 24" o.c. — the same numbers the DeckFrame app computes from published NDS design values following the 2021 IRC R507.6 method at its 40 psf live / 10 psf dead basis (L/360).

Download the chart in a sample permit PDFSample deck plans for permit

Southern Pine No.2 (SP)

Joist size12" o.c.16" o.c.24" o.c.
2x69'-7"8'-4"6'-9"
2x812'-8"10'-11"8'-11"
2x1016'-2"14'-0"11'-5"
2x1218'-0"17'-0"13'-11"

Spruce-Pine-Fir No.2 (SPF)

Joist size12" o.c.16" o.c.24" o.c.
2x68'-3"7'-2"5'-10"
2x810'-11"9'-5"7'-8"
2x1013'-11"12'-1"9'-10"
2x1216'-11"14'-8"12'-0"

Douglas Fir-Larch No.2 (DF-L)

Joist size12" o.c.16" o.c.24" o.c.
2x68'-9"7'-6"6'-2"
2x811'-6"9'-11"8'-1"
2x1014'-8"12'-9"10'-4"
2x1217'-10"15'-6"12'-7"

Hem-Fir No.2 (HF)

Joist size12" o.c.16" o.c.24" o.c.
2x68'-1"7'-0"5'-8"
2x810'-8"9'-2"7'-6"
2x1013'-7"11'-9"9'-7"
2x1216'-6"14'-4"11'-8"

How to read this chart

Spans are horizontal clear spans for single-span deck joists at 40 psf live + 10 psf dead, deflection limited to L/360, computed from published NDS reference design values following the 2021 IRC R507.6 method. Values are capped at the app's 18 ft prescriptive scope. Because they are computed rather than copied, some cells are slightly more conservative than published span tables — the DeckFrame app shows the citation and math behind every number.

Higher ground snow (50/60/70 psf bands), cantilevers, beam sizing, footing diameters, and the ledger fastener schedule all change the answer — the DeckFrame deck joist span calculator solves the whole load path at once and exports it as a cited PDF plan set.

This chart is a planning aid, not a substitute for a qualified professional, your locally adopted code and amendments, or AHJ review. IRC is a trademark of the International Code Council. NDS and DCA6 are publications of the American Wood Council. Not affiliated with or endorsed by ICC or AWC.