Deck Joist Span Calculator (IRC Span Chart for 2x6, 2x8, 2x10, 2x12)

Quick answer: under the IRC deck joist table, a 2x8 joist at 16" on center spans up to 11'-10" in Southern pine and 11'-1" in Douglas fir, hem-fir or SPF. A 2x10 at 16" reaches 14'-0" and 13'-7". Use the calculator below for your exact lumber.

Deck joist span calculator

Lumber species Southern pine Douglas fir-larch, hem-fir, SPF Redwood, western cedar, ponderosa / red pine

Joist size 2x62x8 2x102x12

Joist spacing (on center) 12 in16 in24 in

Optional: span you need (ft)

Based on 40 psf live load + 10 psf dead load, No. 2 grade or better, wet service (IRC 2021 Table R507.6). If your area's ground snow load is above 40 psf, spans are shorter. Always check your local building department.

Deck joist span chart (IRC)

Maximum joist span, measured from the face of one support to the face of the next. The highlighted cell matches the calculator.

How to read your result

• Span is the clear distance between the ledger (or beam) and the next beam, not the overall deck depth.
• Closer spacing = longer span. Going from 16" to 12" on center adds roughly 1 to 2 feet.
• Composite decking often requires 12" or 16" spacing regardless of span. Check the decking maker's rules.
• Cantilevers (joists running past the beam) have their own limits. Keep any cantilever to a quarter of the back span or less unless your local code says otherwise.

Common questions

How far can a 2x8 deck joist span?

At 16" on center: 11'-10" (Southern pine), 11'-1" (Douglas fir-larch, hem-fir, SPF) or 10'-7" (redwood and cedar). At 24" on center the span drops to roughly 8'-8" to 9'-8".

How far can a 2x10 deck joist span?

At 16" on center: 14'-0" (Southern pine), 13'-7" (Douglas fir, hem-fir, SPF) or 13'-0" (redwood and cedar).

Can I use the floor joist table for a deck?

No. Decks are outdoors, so the wood is wetter and weaker. The deck table already accounts for that, and its spans are shorter than indoor floor joist spans.

What if my span is longer than the table allows?

Use a bigger joist, tighter spacing, or add a beam in the middle so each joist spans less.

Checked by: Engr. Abdul Latif, civil and structural engineer. Values follow the International Residential Code deck joist table and the AWC DCA 6 deck guide. This calculator gives estimates for planning only. Your local building code and inspector have the final say.