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

Source

Span values follow the floor and deck joist tables in the International Residential Code, using SPF at 10 psf dead load and 40 psf live load. Table citations: International Code Council; design values per the American Wood Council National Design Specification.

Related tools

• Joist span
• Deck boards
• Full deck bundle