Deck Joist Span Calculator (IRC R507.6)
How far can a deck joist span? It depends on the joist size, the on-center spacing and the lumber species. Enter your deck below and the calculator reads the maximum span straight from IRC Table R507.6 — the same table your plans examiner uses.
Member sizes read from the IRC R507.6 (joists) and R507.5 (beams) tables for No. 2 Southern Pineat 40 psf live + 10 psf dead. Footings from tributary load ÷ soil bearing (R507.3); ledger fasteners per R507.9. Confirm with your local building department.
| Decking — Pressure-treated pine192 sq ft · ~28 × 16′ boards | $575–$1,730 |
| Substructure (joists, beam, posts, hardware)192 sq ft framing | $1,150–$2,495 |
| Footings (concrete piers)4 posts | $140–$360 |
| Railing / guard40 lin ft | $600–$2,400 |
| Stairs4 treads | $120–$380 |
| Permit + fasteners + miscallowance | $75–$500 |
| Total estimate | $2,660–$7,865 |
Low = DIY material budget; high = contractor-installed (labor included). Regional prices vary — treat as a planning range, not a quote.
Full deck joist span table (IRC R507.6)
| Joist | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2x6 | 9'11" | 9' | 7'7" |
| 2x8 | 13'1" | 11'10" | 9'8" |
| 2x10 | 16'2" | 14' | 11'5" |
| 2x12 | 18' | 16'6" | 13'6" |
| Joist | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2x6 | 9'6" | 8'4" | 6'10" |
| 2x8 | 12'6" | 11'1" | 9'1" |
| 2x10 | 15'8" | 13'7" | 11'1" |
| 2x12 | 18' | 15'9" | 12'10" |
| Joist | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2x6 | 8'10" | 8' | 6'10" |
| 2x8 | 11'8" | 10'7" | 8'8" |
| 2x10 | 14'11" | 13' | 10'7" |
| 2x12 | 17'5" | 15'1" | 12'4" |
Deck Joist Span — what to know
- •Spans are clear, face-of-support to face-of-support, for No. 2 grade lumber at 40 psf live + 10 psf dead load.
- •Tighter spacing spans further: a 2x8 Southern Pine goes 13'1" at 12" o.c. but only 9'8" at 24" o.c.
- •Joist cantilevers past the beam are limited to 1/4 of the back-span (IRC R507.6.1).
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