Joist Span Chart

This is the table to check before you buy joists. Span is not a matter of opinion — a joist that is too long for its spacing is the most common structural mistake in amateur deck and floor builds.

Joist	12" OC	16" OC	24" OC
2 × 6	10'-6"	9'-10"	8'-5"
2 × 8	13'-6"	12'-7"	10'-11"
2 × 10	16'-3"	15'-1"	13'-3"
2 × 12	19'-1"	17'-9"	15'-8"

Values are for SPF (spruce-pine-fir) at typical residential loads (40 psf live load, 3 ft snow). Southern pine and Douglas fir span longer at the same size and spacing. Check the grade stamp — lumber manufacturers publish actual allowable spans for their product, and that number governs.

Reading the table

• Clear span is the distance between supports, not the length of the board. A joist bearing on a wall and a beam has a clear span equal to the gap between them, but is cut longer.
• Overhang is not included in these numbers. The tail beyond the last support is a cantilever and has its own limits — usually one-third of the span back to the last bearing.
• Beams change everything. Doubling joists does not extend their span. If you need more reach, add a beam or post.

When the table is not enough

Live loads above 40 psf (garage floor with a car, heavy storage), snow loads above 3 ft, or spans over 20 feet all require an engineered design. Many jurisdictions require an engineer's stamp on decks over a certain height or square footage.

Where to buy

Compare current pricing across major suppliers — prices vary by region and season.

2x6 pressure treated joist 2x8 framing lumber joist hanger beam 6x6

Related tools

• Joist span
• Deck boards
• Full deck bundle