1. What this table is (and is not)
This is a reference table for sizing solid-sawn wood deck joists under the prescriptive provisions of the International Residential Code (IRC), 2024 edition, Table R507.6. It answers one question: for a given species group, joist size, and on-center spacing, how far can a single, simply-supported deck joist span?
[Guessing]
2. Deck joist span table
Spans assume a live load of 40 psf plus a dead load of 10 psf, and a deflection limit of L/360 for the main span (L/180 at the cantilever tip under a 220 lb point load). These are the standard IRC deck design assumptions — not a heavier snow-load or commercial-use case.
| Joist size | 12" o.c. | 16" o.c. | 24" o.c. | Max cantilever |
|---|---|---|---|---|
| 2×6 | 9'-11" | 9'-0" | 7'-7" | 6'-8" |
| 2×8 | 13'-1" | 11'-10" | 9'-8" | 10'-1" |
| 2×10 | 16'-2" | 14'-0" | 11'-5" | 14'-6" |
| 2×12 | 18'-0" | 16'-6" | 13'-6" | 18'-0" |
| Joist size | 12" o.c. | 16" o.c. | 24" o.c. | Max cantilever |
|---|---|---|---|---|
| 2×6 | 9'-6" | 8'-8" | 7'-2" | 6'-3" |
| 2×8 | 12'-6" | 11'-1" | 9'-1" | 9'-5" |
| 2×10 | 15'-8" | 13'-7" | 11'-1" | 13'-7" |
| 2×12 | 18'-0" | 15'-9" | 12'-10" | 18'-0" |
| Joist size | 12" o.c. | 16" o.c. | 24" o.c. | Max cantilever |
|---|---|---|---|---|
| 2×6 | 8'-10" | 8'-0" | 7'-0" | 5'-7" |
| 2×8 | 11'-8" | 10'-7" | 8'-8" | 8'-6" |
| 2×10 | 14'-11" | 13'-0" | 10'-7" | 12'-3" |
| 2×12 | 17'-5" | 15'-1" | 12'-4" | 16'-5" |
3. The cantilever rule
The maximum cantilever for a given joist is the lesser of one-fourth of the actual joist span you are using, or the "Max cantilever" value in the table above for that species/size/spacing. The table value is a ceiling, not a guarantee — a joist run at a shorter span than its table maximum has a shorter allowable cantilever too, even though the table only shows the cantilever at the table's own maximum span.
4. What this table does not cover
- Beam sizing. IRC 2024 Table R507.5 (deck beams) restructured its column headings from the 2021 edition to combine joist-span-and-cantilever combinations into shared columns. We have not been able to source the complete, verified 2024 table yet, so it is intentionally not published here. Size beams from your own calculation or a source you can verify directly.
- Footing depth. The IRC does not set a national frost depth — see the footing depth by frost line guide for why, and how to find your local requirement.
- Species and grades outside the three groups shown. The full IRC table lists more species/grade combinations than reproduced here.
- Multi-span (continuous over an intermediate beam) joists, engineered lumber (I-joists, LVL), or ground snow loads above what a 40 psf live load represents. Those require their own manufacturer span tables or an engineer's calculation.
5. Using it with the joist calculator
Once you know your allowable span for a chosen species/size/spacing, use the deck joist calculator to get joist quantity and total linear length for your actual deck dimensions — that calculator takes span and spacing as inputs you already know; it does not size joists itself, by design, for the same reason this table needs its own edition/jurisdiction caveat above.