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?
Check your code edition
2. Deck joist span table
Allowable spans below are for a 40 psf live load plus a 10 psf dead load, No. 2 grade lumber, and a deflection limit of L/360 at the main span. IRC 2024 Table R507.6 also has separate rows for ground snow loads of 50, 60, and 70 psf with shorter spans; they are not reproduced here. If your area has a ground snow load above 40 psf, use the code table for your load, not this one.
| Joist size | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2×6 | 9'-11" | 9'-0" | 7'-7" |
| 2×8 | 13'-1" | 11'-10" | 9'-8" |
| 2×10 | 16'-2" | 14'-0" | 11'-5" |
| 2×12 | 18'-0" | 16'-6" | 13'-6" |
| Joist size | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2×6 | 9'-6" | 8'-4" | 6'-10" |
| 2×8 | 12'-6" | 11'-1" | 9'-1" |
| 2×10 | 15'-8" | 13'-7" | 11'-1" |
| 2×12 | 18'-0" | 15'-9" | 12'-10" |
| Joist size | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2×6 | 8'-10" | 8'-0" | 6'-10" |
| 2×8 | 11'-8" | 10'-7" | 8'-8" |
| 2×10 | 14'-11" | 13'-0" | 10'-7" |
| 2×12 | 17'-5" | 15'-1" | 12'-4" |
3. Maximum cantilever
In the 2024 IRC the allowable cantilever depends on the joist back span: the length of joist on the house side of the beam that the cantilever hangs past. Find your joist size and back span in the table for your species group. Interpolating between back-span columns is allowed; extrapolating beyond them is not. NP means a cantilever is not permitted at that back span.
Cantilevers are short
| Joist size | 4 ft | 6 ft | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft | 18 ft |
|---|---|---|---|---|---|---|---|---|
| 2×6 | 1'-0" | 1'-6" | 1'-5" | NP | NP | NP | NP | NP |
| 2×8 | 1'-0" | 1'-6" | 2'-0" | 2'-6" | 2'-3" | NP | NP | NP |
| 2×10 | 1'-0" | 1'-6" | 2'-0" | 2'-6" | 3'-0" | 3'-4" | 3'-4" | NP |
| 2×12 | 1'-0" | 1'-6" | 2'-0" | 2'-6" | 3'-0" | 3'-6" | 4'-0" | 4'-1" |
| Joist size | 4 ft | 6 ft | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft | 18 ft |
|---|---|---|---|---|---|---|---|---|
| 2×6 | 1'-0" | 1'-6" | 1'-4" | NP | NP | NP | NP | NP |
| 2×8 | 1'-0" | 1'-6" | 2'-0" | 2'-3" | 2'-0" | NP | NP | NP |
| 2×10 | 1'-0" | 1'-6" | 2'-0" | 2'-6" | 3'-0" | 3'-3" | NP | NP |
| 2×12 | 1'-0" | 1'-6" | 2'-0" | 2'-6" | 3'-0" | 3'-6" | 3'-11" | 3'-11" |
| Joist size | 4 ft | 6 ft | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft | 18 ft |
|---|---|---|---|---|---|---|---|---|
| 2×6 | 1'-0" | 1'-4" | 1'-1" | NP | NP | NP | NP | NP |
| 2×8 | 1'-0" | 1'-6" | 2'-0" | 1'-11" | NP | NP | NP | NP |
| 2×10 | 1'-0" | 1'-6" | 2'-0" | 2'-6" | 3'-0" | 2'-9" | NP | NP |
| 2×12 | 1'-0" | 1'-6" | 2'-0" | 2'-6" | 3'-0" | 3'-6" | 3'-8" | NP |
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.