2×12 floor joist spans (2021 IRC)
Every allowable span the 2021 International Residential Code floor tables list for a 2×12 joist — four species, four grades, four spacings, both load cases — each table cited where it sits.
2021 IRC Table R502.3.1(2) covers residential living areas; 2021 IRC Table R502.3.1(1) covers residential sleeping areas. Both tables are below, in that order.
A 2×12 Southern pine No. 2 floor joist at 16-inch centers spans up to 16’6” under standard residential living-area loads (2021 IRC Table R502.3.1(2)). Widen the spacing to 24-inch centers and the same joist is listed at 13’6”; hold 16-inch centers and switch to Spruce-pine-fir No. 2 and the table lists 17’10”. Under 2021 IRC Table R502.3.1(1) — residential sleeping areas, 30 psf live / 10 psf dead / L/360 — that same Southern pine No. 2 at 16 inches is listed at 18’6”.
2×12 floor joists — residential living areas
| 2×12 — species and grade | 12" on center | 16" on center | 19.2" on center | 24" on center |
|---|---|---|---|---|
| Douglas fir-larch Select Structural | 23’3” | 21’1” | 19’10” | 18’5” |
| Douglas fir-larch No. 1 | 22’0” | 19’1” | 17’5” | 15’7” |
| Douglas fir-larch No. 2 | 20’11” | 18’1” | 16’6” | 14’9” |
| Douglas fir-larch No. 3 | 16’0” | 13’10” | 12’7” | 11’3” |
| Hem-fir Select Structural | 21’11” | 19’11” | 18’9” | 17’5” |
| Hem-fir No. 1 | 21’6” | 18’10” | 17’2” | 15’5” |
| Hem-fir No. 2 | 20’4” | 17’7” | 16’1” | 14’4” |
| Hem-fir No. 3 | 15’7” | 13’6” | 12’4” | 11’0” |
| Southern pine Select Structural | 22’10” | 20’9” | 19’6” | 18’1” |
| Southern pine No. 1 | 21’11” | 19’1” | 17’5” | 15’7” |
| Southern pine No. 2 | 19’1” | 16’6” | 15’1” | 13’6” |
| Southern pine No. 3 | 14’9” | 12’10” | 11’8” | 10’5” |
| Spruce-pine-fir Select Structural | 21’6” | 19’6” | 18’4” | 17’0” |
| Spruce-pine-fir No. 1 | 20’7” | 17’10” | 16’3” | 14’7” |
| Spruce-pine-fir No. 2 | 20’7” | 17’10” | 16’3” | 14’7” |
| Spruce-pine-fir No. 3 | 15’7” | 13’6” | 12’4” | 11’0” |
2021 IRC Table R502.3.1(2) — residential living areas, 40 psf live / 10 psf dead / L/360. table source
2×12 floor joists — residential sleeping areas
| 2×12 — species and grade | 12" on center | 16" on center | 19.2" on center | 24" on center |
|---|---|---|---|---|
| Douglas fir-larch Select Structural | 25’7” | 23’3” | 21’10” | 20’3” |
| Douglas fir-larch No. 1 | 24’8” | 21’4” | 19’6” | 17’5” |
| Douglas fir-larch No. 2 | 23’4” | 20’3” | 18’6” | 16’6” |
| Douglas fir-larch No. 3 | 17’10” | 15’5” | 14’1” | 12’7” |
| Hem-fir Select Structural | 24’2” | 21’11” | 20’8” | 19’2” |
| Hem-fir No. 1 | 23’7” | 21’1” | 19’3” | 17’2” |
| Hem-fir No. 2 | 22’6” | 19’8” | 17’1” | 16’1” |
| Hem-fir No. 3 | 17’5” | 15’1” | 13’9” | 12’4” |
| Southern pine Select Structural | 25’1” | 22’10” | 21’6” | 19’11” |
| Southern pine No. 1 | 24’2” | 21’4” | 19’6” | 17’5” |
| Southern pine No. 2 | 21’4” | 18’6” | 16’10” | 15’1” |
| Southern pine No. 3 | 16’6” | 14’4” | 13’1” | 11’8” |
| Spruce-pine-fir Select Structural | 23’7” | 21’6” | 20’2” | 18’9” |
| Spruce-pine-fir No. 1 | 23’0” | 19’11” | 18’3” | 16’3” |
| Spruce-pine-fir No. 2 | 23’0” | 19’11” | 18’3” | 16’3” |
| Spruce-pine-fir No. 3 | 17’5” | 15’1” | 13’9” | 12’4” |
2021 IRC Table R502.3.1(1) — residential sleeping areas, 30 psf live / 10 psf dead / L/360. table source
What these tables state
Each number is the span the code table lists for that species, grade, and on-center spacing at the load case stamped at the top of this page: 40 psf live / 10 psf dead / L/360 for residential living areas, 30 psf live / 10 psf dead / L/360 for residential sleeping areas. Change the spacing, the grade, or the species and you are reading a different cell of the same table.
Point loads, cantilevers beyond the table footnotes, unusual snow loads, or anything else outside the table's stated conditions — that's an engineer's question.
Other sizes and assemblies
Other floor joist sizes: 2×6 floor joists · 2×8 floor joists · 2×10 floor joists
The same 2×12 in other assemblies: 2×12 rafters · 2×12 deck joists
Common questions
Can 2×12 floor joists span 19 feet?
At 16-inch centers, 2×12 Southern pine No. 2 is listed at 16’6” in 2021 IRC Table R502.3.1(2) (40 psf live / 10 psf dead / L/360). 20 of the 64 2×12 cells in that table are 19 feet or longer, and the widest spacing among them is 19.2-inch centers — Southern pine Select Structural at 19.2 inches is listed at 19’6”.
How far can a 2×12 floor joist span at 24-inch centers?
2021 IRC Table R502.3.1(2) — residential living areas — lists 2×12 No. 2 at 24-inch centers as Douglas fir-larch 14’9”, Hem-fir 14’4”, Southern pine 13’6”, Spruce-pine-fir 14’7”. The same four species in 2021 IRC Table R502.3.1(1) (residential sleeping areas): 16’6”, 16’1”, 15’1”, 16’3”.
What is the difference between the two 2021 IRC floor joist tables for a 2×12?
2021 IRC Table R502.3.1(1) covers residential sleeping areas at 30 psf live / 10 psf dead / L/360; 2021 IRC Table R502.3.1(2) covers residential living areas at 40 psf live / 10 psf dead / L/360. Same 2×12 Southern pine No. 2 at 16-inch centers: 18’6” in the first, 16’6” in the second.