Floor Joist Span Calculator
Check how far a floor joist can span for its species, size, spacing and floor use, and see span charts for 40 psf living areas and 30 psf bedrooms.
Douglas fir-larch No. 2 floor joists at 16 in on center (40 psf live, 10 psf dead, L/360) span about: 2×6 9′9″, 2×8 12′9″, 2×10 15′7″ and 2×12 18′1″. Bedrooms (30 psf) allow longer spans; tile floors are best designed to L/480 or stiffer.
Floor joist span chart: living areas (40 psf live, 10 psf dead, L/360)
| Joist | Douglas fir-larch | Southern pine | Hem-fir | Spruce-pine-fir |
|---|---|---|---|---|
| 2×6 at 12 in | 10′9″ | 10′3″ | 10′0″ | 10′3″ |
| 2×6 at 16 in | 9′9″ | 9′4″ | 9′1″ | 9′4″ |
| 2×6 at 24 in | 8′3″ | 7′7″ | 7′11″ | 8′1″ |
| 2×8 at 12 in | 14′2″ | 13′6″ | 13′2″ | 13′6″ |
| 2×8 at 16 in | 12′9″ | 11′10″ | 12′0″ | 12′3″ |
| 2×8 at 24 in | 10′5″ | 9′8″ | 10′2″ | 10′3″ |
| 2×10 at 12 in | 18′0″ | 16′2″ | 16′10″ | 17′3″ |
| 2×10 at 16 in | 15′7″ | 14′0″ | 15′2″ | 15′5″ |
| 2×10 at 24 in | 12′9″ | 11′5″ | 12′5″ | 12′7″ |
| 2×12 at 12 in | 20′11″ | 19′1″ | 20′4″ | 20′7″ |
| 2×12 at 16 in | 18′1″ | 16′6″ | 17′7″ | 17′10″ |
| 2×12 at 24 in | 14′9″ | 13′6″ | 14′4″ | 14′7″ |
Floor joist span chart: bedrooms (30 psf live, 10 psf dead, L/360)
| Joist | Douglas fir-larch | Southern pine | Hem-fir | Spruce-pine-fir |
|---|---|---|---|---|
| 2×6 at 12 in | 11′10″ | 11′3″ | 11′0″ | 11′3″ |
| 2×6 at 16 in | 10′9″ | 10′3″ | 10′0″ | 10′3″ |
| 2×6 at 24 in | 9′3″ | 8′6″ | 8′9″ | 8′11″ |
| 2×8 at 12 in | 15′7″ | 14′11″ | 14′6″ | 14′11″ |
| 2×8 at 16 in | 14′2″ | 13′3″ | 13′2″ | 13′6″ |
| 2×8 at 24 in | 11′8″ | 10′10″ | 11′4″ | 11′6″ |
| 2×10 at 12 in | 19′10″ | 18′1″ | 18′6″ | 19′0″ |
| 2×10 at 16 in | 17′5″ | 15′8″ | 16′10″ | 17′2″ |
| 2×10 at 24 in | 14′3″ | 12′10″ | 13′10″ | 14′1″ |
| 2×12 at 12 in | 23′4″ | 21′4″ | 22′6″ | 23′0″ |
| 2×12 at 16 in | 20′3″ | 18′6″ | 19′8″ | 19′11″ |
| 2×12 at 24 in | 16′6″ | 15′1″ | 16′1″ | 16′3″ |
Frequently asked questions
How far can a 2×8 floor joist span?
About 12′9″ for Douglas fir-larch No. 2 at 16 in on center under a 40 psf living-area load. Southern pine and SPF are similar; hem-fir is a little shorter.
How far can a 2×10 floor joist span?
About 15′7″ for Douglas fir-larch No. 2 at 16 in on center (40 psf live load).
How far can a 2×12 floor joist span?
About 18′1″ for Douglas fir-larch No. 2 at 16 in on center (40 psf live load).
How far can a 2×6 floor joist span?
About 9′9″ for Douglas fir-larch No. 2 at 16 in on center; 2×6 floors are mostly used for sheds and small additions.
What is L/360?
The floor may bend no more than its span divided by 360 under the full live load: about ½ in for a 15 ft joist. Tile and stone floors are usually designed to L/480 or stiffer to avoid cracking.
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Spans are the smallest of the bending, live-load deflection and shear limits using NDS 2018 design values for No. 2 dimension lumber with the repetitive-member factor 1.15, dry service, the method behind the AWC span tables and IRC Table R502.3.1. Values may differ slightly from your code book's table. Engineered I-joists and LVL use the maker's tables.