Deck Joist Span Calculator
Find how far your deck joists can span for their species, size and spacing, check a planned span, and see the full span chart, using the same checks as the AWC DCA 6 deck guide.
Southern pine No. 2 deck joists at 16 in on center span about: 2×6 9′0″, 2×8 11′10″, 2×10 14′0″ and 2×12 16′6″ (40 psf live + 10 psf dead load, L/360, wet service). Treated Douglas fir, hem-fir and SPF are usually incised, which shortens their spans. Joists may cantilever about ¼ of their span past the beam.
Deck joist span chart
No. 2 grade, 40 psf live + 10 psf dead load, L/360, wet service; Douglas fir, hem-fir and SPF incised. Spans capped at 18 ft as in DCA 6.
| Joist | Southern pine | Douglas fir-larch | Hem-fir | Spruce-pine-fir | Western cedars |
|---|---|---|---|---|---|
| 2×6 at 12 in | 9′11″ | 9′7″ | 9′6″ | 9′9″ | 8′10″ |
| 2×6 at 16 in | 9′0″ | 8′4″ | 8′8″ | 8′10″ | 8′0″ |
| 2×6 at 24 in | 7′7″ | 6′10″ | 7′2″ | 7′3″ | 7′0″ |
| 2×8 at 12 in | 13′1″ | 13′2″ | 12′6″ | 12′10″ | 11′8″ |
| 2×8 at 16 in | 11′10″ | 11′5″ | 11′1″ | 11′3″ | 10′7″ |
| 2×8 at 24 in | 9′8″ | 9′4″ | 9′1″ | 9′2″ | 9′2″ |
| 2×10 at 12 in | 16′2″ | 16′1″ | 15′8″ | 15′11″ | 14′11″ |
| 2×10 at 16 in | 14′0″ | 13′11″ | 13′7″ | 13′9″ | 13′6″ |
| 2×10 at 24 in | 11′5″ | 11′5″ | 11′1″ | 11′3″ | 11′3″ |
| 2×12 at 12 in | 18′0″ | 18′0″ | 18′0″ | 18′0″ | 18′0″ |
| 2×12 at 16 in | 16′6″ | 16′2″ | 15′9″ | 16′0″ | 16′0″ |
| 2×12 at 24 in | 13′6″ | 13′3″ | 12′10″ | 13′0″ | 13′0″ |
Deck framing tips
- Spans are measured between the ledger or beam supports, not end to end.
- 16 in on center is standard; composite decking often needs 12 in, and diagonal decking 12 in.
- Hot tubs, heavy planters and privacy walls add point loads; those need an engineered design.
Frequently asked questions
How far can a 2×8 deck joist span?
About 11′10″ for southern pine No. 2 at 16 in on center, and less for incised hem-fir or SPF. At 12 in spacing it spans further; at 24 in, less.
How far can a 2×10 deck joist span?
About 14′0″ for southern pine No. 2 at 16 in on center (40 psf live load).
How far can a 2×6 deck joist span?
About 9′0″ for southern pine No. 2 at 16 in on center. 2×6 joists suit low, small decks.
How far can a deck joist cantilever?
Up to about one-quarter of the joist's back span, and DCA 6 caps it further for some sizes. A 12 ft joist span allows about a 3 ft cantilever.
Why are treated hem-fir and SPF spans shorter?
These species are incised (slit) so the preservative can penetrate, and incising lowers their strength and stiffness. Southern pine takes treatment without incising.
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Allowable span is the smallest of the bending, deflection (L/360 under live load) and shear limits using NDS 2018 design values for No. 2 lumber, the repetitive-member factor 1.15, wet-service factors (bending 0.85 where FbCF > 1,150 psi, E 0.9, shear 0.97) and incising factors (0.8, 0.95, 0.8), as in AWC DCA 6; results match DCA 6 Table 2 within an inch. Your local code and inspector have the final say.