Floor joist span calculator: how far can a floor joist span?
15 ft 7 in
maximum span, 2 × 10 at 16 in on center · 18 ft 0 in at 12 in · 14 ft 3 in at 19.2 in · 12 ft 9 in at 24 in · for Douglas fir-larch #2, IRC Table R502.3.1
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
15 ft 7 in
maximum span, 2 × 10 at 16 in on center · 18 ft 0 in at 12 in · 14 ft 3 in at 19.2 in · 12 ft 9 in at 24 in
Source: IRC 2021 Tables R502.3.1(1) and R502.3.1(2), Floor Joist Spans for Common Lumber Species (International Code Council), read October 17, 2026. Read the source
A 2 × 10 Douglas fir-larch No. 2 floor joist at 16 inches on center spans up to 15 ft 7 in under a living area's 40 psf live load (IRC 2021 Table R502.3.1(2)), and 17 ft 5 in under a bedroom's 30 psf.
A worked example
A 2 × 8 Southern pine No. 1 joist at 19.2 in on center under a bedroom, with a 20 psf dead load needs 12 ft 7 in. That is the Table R502.3.1(1) cell for 30 psf live load, 19.2 in spacing, Southern pine No. 1, 2 × 8 and 20 psf dead load; with a 10 psf dead load the same joist spans 13 ft 4 in.
How far can a 2x10 floor joist span?
At 16 inches on center under a living area, from 10 ft 10 in to 17 ft 4 in, depending on species and grade: 17 ft 4 in in Douglas fir-larch select structural, 15 ft 7 in in Douglas fir-larch No. 2 and 14 ft 0 in in Southern pine No. 2, at a 10 psf dead load. Grade No. 3 is shortest, 10 ft 10 in in Southern pine. Pick your lumber above to get its cell.
How far can a 2x8 floor joist span?
A 2 × 8 Douglas fir-larch No. 2 joist spans 12 ft 9 in at 16 inches on center under a living area and 14 ft 2 in at 12 inches, at a 10 psf dead load. A 2 × 6 in the same lumber spans 9 ft 9 in at 16 inches. Under a bedroom, the lighter 30 psf live load lets each size run longer.
Should I use a 10 or 20 psf dead load?
The dead load is the weight of the floor itself: joists, subfloor and finish. The IRC gives each span for 10 psf and for 20 psf, and the heavier column is shorter, sometimes by a foot or more: a 2 × 12 Douglas fir-larch No. 2 at 16 inches spans 18 ft 1 in at 10 psf and 16 ft 6 in at 20 psf under a living area. A tile floor on a mortar bed is the usual reason to read the 20 psf column.
What else it is called
A floor joist span calculator is also searched as a floor joist span chart or table, or as “how far can a 2x10 floor joist span”. The span is the clear distance between supports; on center (o.c.) is the distance from the middle of one joist to the middle of the next, and 19.2 in puts five joists in every 8 ft.
The full IRC table
| Live load · spacing · species and grade | 2 × 6, 10 psf dead | 2 × 8, 10 psf dead | 2 × 10, 10 psf dead | 2 × 12, 10 psf dead | 2 × 6, 20 psf dead | 2 × 8, 20 psf dead | 2 × 10, 20 psf dead | 2 × 12, 20 psf dead |
|---|---|---|---|---|---|---|---|---|
| 30 psf · 12 in · Douglas fir-larch SS | 12-6 | 16-6 | 21-0 | 25-7 | 12-6 | 16-6 | 21-0 | 25-7 |
| 30 psf · 12 in · Douglas fir-larch #1 | 12-0 | 15-10 | 20-3 | 24-8 | 12-0 | 15-7 | 19-0 | 22-0 |
| 30 psf · 12 in · Douglas fir-larch #2 | 11-10 | 15-7 | 19-10 | 23-4 | 11-8 | 14-9 | 18-0 | 20-11 |
| 30 psf · 12 in · Douglas fir-larch #3 | 9-11 | 12-7 | 15-5 | 17-10 | 8-11 | 11-3 | 13-9 | 16-0 |
| 30 psf · 12 in · Hem-fir SS | 11-10 | 15-7 | 19-10 | 24-2 | 11-10 | 15-7 | 19-10 | 24-2 |
| 30 psf · 12 in · Hem-fir #1 | 11-7 | 15-3 | 19-5 | 23-7 | 11-7 | 15-3 | 18-9 | 21-9 |
| 30 psf · 12 in · Hem-fir #2 | 11-0 | 14-6 | 18-6 | 22-6 | 11-0 | 14-4 | 17-6 | 20-4 |
| 30 psf · 12 in · Hem-fir #3 | 9-8 | 12-4 | 15-0 | 17-5 | 8-8 | 11-0 | 13-5 | 15-7 |
| 30 psf · 12 in · Southern pine SS | 12-3 | 16-2 | 20-8 | 25-1 | 12-3 | 16-2 | 20-8 | 25-1 |
| 30 psf · 12 in · Southern pine #1 | 11-10 | 15-7 | 19-10 | 24-2 | 11-10 | 15-7 | 18-7 | 22-0 |
| 30 psf · 12 in · Southern pine #2 | 11-3 | 14-11 | 18-1 | 21-4 | 10-9 | 13-8 | 16-2 | 19-1 |
| 30 psf · 12 in · Southern pine #3 | 9-2 | 11-6 | 14-0 | 16-6 | 8-2 | 10-3 | 12-6 | 14-9 |
| 30 psf · 12 in · Spruce-pine-fir SS | 11-7 | 15-3 | 19-5 | 23-7 | 11-7 | 15-3 | 19-5 | 23-7 |
| 30 psf · 12 in · Spruce-pine-fir #1 | 11-3 | 14-11 | 19-0 | 23-0 | 11-3 | 14-7 | 17-9 | 20-7 |
| 30 psf · 12 in · Spruce-pine-fir #2 | 11-3 | 14-11 | 19-0 | 23-0 | 11-3 | 14-7 | 17-9 | 20-7 |
| 30 psf · 12 in · Spruce-pine-fir #3 | 9-8 | 12-4 | 15-0 | 17-5 | 8-8 | 11-0 | 13-5 | 15-7 |
| 30 psf · 16 in · Douglas fir-larch SS | 11-4 | 15-0 | 19-1 | 23-3 | 11-4 | 15-0 | 19-1 | 23-3 |
| 30 psf · 16 in · Douglas fir-larch #1 | 10-11 | 14-5 | 18-5 | 21-4 | 10-8 | 13-6 | 16-5 | 19-1 |
| 30 psf · 16 in · Douglas fir-larch #2 | 10-9 | 14-2 | 17-5 | 20-3 | 10-1 | 12-9 | 15-7 | 18-1 |
| 30 psf · 16 in · Douglas fir-larch #3 | 8-7 | 10-11 | 13-4 | 15-5 | 7-8 | 9-9 | 11-11 | 13-10 |
| 30 psf · 16 in · Hem-fir SS | 10-9 | 14-2 | 18-0 | 21-11 | 10-9 | 14-2 | 18-0 | 21-11 |
| 30 psf · 16 in · Hem-fir #1 | 10-6 | 13-10 | 17-8 | 21-1 | 10-6 | 13-4 | 16-3 | 18-10 |
| 30 psf · 16 in · Hem-fir #2 | 10-0 | 13-2 | 16-10 | 19-8 | 9-10 | 12-5 | 15-2 | 17-7 |
| 30 psf · 16 in · Hem-fir #3 | 8-5 | 10-8 | 13-0 | 15-1 | 7-6 | 9-6 | 11-8 | 13-6 |
| 30 psf · 16 in · Southern pine SS | 11-2 | 14-8 | 18-9 | 22-10 | 11-2 | 14-8 | 18-9 | 22-10 |
| 30 psf · 16 in · Southern pine #1 | 10-9 | 14-2 | 18-0 | 21-4 | 10-9 | 13-9 | 16-1 | 19-1 |
| 30 psf · 16 in · Southern pine #2 | 10-3 | 13-3 | 15-8 | 18-6 | 9-4 | 11-10 | 14-0 | 16-6 |
| 30 psf · 16 in · Southern pine #3 | 7-11 | 10-0 | 11-1 | 14-4 | 7-1 | 8-11 | 10-10 | 12-10 |
| 30 psf · 16 in · Spruce-pine-fir SS | 10-6 | 13-10 | 17-8 | 21-6 | 10-6 | 13-10 | 17-8 | 21-4 |
| 30 psf · 16 in · Spruce-pine-fir #1 | 10-3 | 13-6 | 17-2 | 19-11 | 9-11 | 12-7 | 15-5 | 17-10 |
| 30 psf · 16 in · Spruce-pine-fir #2 | 10-3 | 13-6 | 17-2 | 19-11 | 9-11 | 12-7 | 15-5 | 17-10 |
| 30 psf · 16 in · Spruce-pine-fir #3 | 8-5 | 10-8 | 13-0 | 15-1 | 7-6 | 9-6 | 11-8 | 13-6 |
| 30 psf · 19.2 in · Douglas fir-larch SS | 10-8 | 14-1 | 18-0 | 21-10 | 10-8 | 14-1 | 18-0 | 21-4 |
| 30 psf · 19.2 in · Douglas fir-larch #1 | 10-4 | 13-7 | 16-9 | 19-6 | 9-8 | 12-4 | 15-0 | 17-5 |
| 30 psf · 19.2 in · Douglas fir-larch #2 | 10-1 | 13-0 | 15-11 | 18-6 | 9-3 | 11-8 | 14-3 | 16-6 |
| 30 psf · 19.2 in · Douglas fir-larch #3 | 7-10 | 10-0 | 12-2 | 14-1 | 7-0 | 8-11 | 10-11 | 12-7 |
| 30 psf · 19.2 in · Hem-fir SS | 10-1 | 13-4 | 17-0 | 20-8 | 10-1 | 13-4 | 17-0 | 20-7 |
| 30 psf · 19.2 in · Hem-fir #1 | 9-10 | 13-0 | 16-7 | 19-3 | 9-7 | 12-2 | 14-10 | 17-2 |
| 30 psf · 19.2 in · Hem-fir #2 | 9-5 | 12-5 | 15-6 | 17-1 | 8-11 | 11-4 | 13-10 | 16-1 |
| 30 psf · 19.2 in · Hem-fir #3 | 7-8 | 9-9 | 11-10 | 13-9 | 6-10 | 8-8 | 10-7 | 12-4 |
| 30 psf · 19.2 in · Southern pine SS | 10-6 | 13-10 | 17-8 | 21-6 | 10-6 | 13-10 | 17-8 | 21-6 |
| 30 psf · 19.2 in · Southern pine #1 | 10-1 | 13-4 | 16-5 | 19-6 | 9-11 | 12-7 | 14-8 | 17-5 |
| 30 psf · 19.2 in · Southern pine #2 | 9-6 | 12-1 | 14-4 | 16-10 | 8-6 | 10-10 | 12-10 | 15-1 |
| 30 psf · 19.2 in · Southern pine #3 | 7-3 | 9-1 | 11-0 | 13-1 | 6-5 | 8-2 | 9-10 | 11-8 |
| 30 psf · 19.2 in · Spruce-pine-fir SS | 9-10 | 13-0 | 16-7 | 20-2 | 9-10 | 13-0 | 16-7 | 19-6 |
| 30 psf · 19.2 in · Spruce-pine-fir #1 | 9-8 | 12-9 | 15-8 | 18-3 | 9-1 | 11-6 | 14-1 | 16-3 |
| 30 psf · 19.2 in · Spruce-pine-fir #2 | 9-8 | 12-9 | 15-8 | 18-3 | 9-1 | 11-6 | 14-1 | 16-3 |
| 30 psf · 19.2 in · Spruce-pine-fir #3 | 7-8 | 9-9 | 11-10 | 13-9 | 6-10 | 8-8 | 10-7 | 12-4 |
| 30 psf · 24 in · Douglas fir-larch SS | 9-11 | 13-1 | 16-8 | 20-3 | 9-11 | 13-1 | 16-5 | 19-1 |
| 30 psf · 24 in · Douglas fir-larch #1 | 9-7 | 12-4 | 15-0 | 17-5 | 8-8 | 11-0 | 13-5 | 15-7 |
| 30 psf · 24 in · Douglas fir-larch #2 | 9-3 | 11-8 | 14-3 | 16-6 | 8-3 | 10-5 | 12-9 | 14-9 |
| 30 psf · 24 in · Douglas fir-larch #3 | 7-0 | 8-11 | 10-11 | 12-7 | 6-3 | 8-0 | 9-9 | 11-3 |
| 30 psf · 24 in · Hem-fir SS | 9-4 | 12-4 | 15-9 | 19-2 | 9-4 | 12-4 | 15-9 | 18-5 |
| 30 psf · 24 in · Hem-fir #1 | 9-2 | 12-1 | 14-10 | 17-2 | 8-7 | 10-10 | 13-3 | 15-5 |
| 30 psf · 24 in · Hem-fir #2 | 8-9 | 11-4 | 13-10 | 16-1 | 8-0 | 10-2 | 12-5 | 14-4 |
| 30 psf · 24 in · Hem-fir #3 | 6-10 | 8-8 | 10-7 | 12-4 | 6-2 | 7-9 | 9-6 | 11-0 |
| 30 psf · 24 in · Southern pine SS | 9-9 | 12-10 | 16-5 | 19-11 | 9-9 | 12-10 | 16-5 | 19-8 |
| 30 psf · 24 in · Southern pine #1 | 9-4 | 12-4 | 14-8 | 17-5 | 8-10 | 11-3 | 13-1 | 15-7 |
| 30 psf · 24 in · Southern pine #2 | 8-6 | 10-10 | 12-10 | 15-1 | 7-7 | 9-8 | 11-5 | 13-6 |
| 30 psf · 24 in · Southern pine #3 | 6-5 | 8-2 | 9-10 | 11-8 | 5-9 | 7-3 | 8-10 | 10-5 |
| 30 psf · 24 in · Spruce-pine-fir SS | 9-2 | 12-1 | 15-5 | 18-9 | 9-2 | 12-1 | 15-0 | 17-5 |
| 30 psf · 24 in · Spruce-pine-fir #1 | 8-11 | 11-6 | 14-1 | 16-3 | 8-1 | 10-3 | 12-7 | 14-7 |
| 30 psf · 24 in · Spruce-pine-fir #2 | 8-11 | 11-6 | 14-1 | 16-3 | 8-1 | 10-3 | 12-7 | 14-7 |
| 30 psf · 24 in · Spruce-pine-fir #3 | 6-10 | 8-8 | 10-7 | 12-4 | 6-2 | 7-9 | 9-6 | 11-0 |
| 40 psf · 12 in · Douglas fir-larch SS | 11-4 | 15-0 | 19-1 | 23-3 | 11-4 | 15-0 | 19-1 | 23-3 |
| 40 psf · 12 in · Douglas fir-larch #1 | 10-11 | 14-5 | 18-5 | 22-0 | 10-11 | 14-2 | 17-4 | 20-1 |
| 40 psf · 12 in · Douglas fir-larch #2 | 10-9 | 14-2 | 18-0 | 20-11 | 10-8 | 13-6 | 16-5 | 19-1 |
| 40 psf · 12 in · Douglas fir-larch #3 | 8-11 | 11-3 | 13-9 | 16-0 | 8-1 | 10-3 | 12-7 | 14-7 |
| 40 psf · 12 in · Hem-fir SS | 10-9 | 14-2 | 18-0 | 21-11 | 10-9 | 14-2 | 18-0 | 21-11 |
| 40 psf · 12 in · Hem-fir #1 | 10-6 | 13-10 | 17-8 | 21-6 | 10-6 | 13-10 | 17-1 | 19-10 |
| 40 psf · 12 in · Hem-fir #2 | 10-0 | 13-2 | 16-10 | 20-4 | 10-0 | 13-1 | 16-0 | 18-6 |
| 40 psf · 12 in · Hem-fir #3 | 8-8 | 11-0 | 13-5 | 15-7 | 7-11 | 10-0 | 12-3 | 14-3 |
| 40 psf · 12 in · Southern pine SS | 11-2 | 14-8 | 18-9 | 22-10 | 11-2 | 14-8 | 18-9 | 22-10 |
| 40 psf · 12 in · Southern pine #1 | 10-9 | 14-2 | 18-0 | 21-11 | 10-9 | 14-2 | 16-11 | 20-1 |
| 40 psf · 12 in · Southern pine #2 | 10-3 | 13-6 | 16-2 | 19-1 | 9-10 | 12-6 | 14-9 | 17-5 |
| 40 psf · 12 in · Southern pine #3 | 8-2 | 10-3 | 12-6 | 14-9 | 7-5 | 9-5 | 11-5 | 13-6 |
| 40 psf · 12 in · Spruce-pine-fir SS | 10-6 | 13-10 | 17-8 | 21-6 | 10-6 | 13-10 | 17-8 | 21-6 |
| 40 psf · 12 in · Spruce-pine-fir #1 | 10-3 | 13-6 | 17-3 | 20-7 | 10-3 | 13-3 | 16-3 | 18-10 |
| 40 psf · 12 in · Spruce-pine-fir #2 | 10-3 | 13-6 | 17-3 | 20-7 | 10-3 | 13-3 | 16-3 | 18-10 |
| 40 psf · 12 in · Spruce-pine-fir #3 | 8-8 | 11-0 | 13-5 | 15-7 | 7-11 | 10-0 | 12-3 | 14-3 |
| 40 psf · 16 in · Douglas fir-larch SS | 10-4 | 13-7 | 17-4 | 21-1 | 10-4 | 13-7 | 17-4 | 21-1 |
| 40 psf · 16 in · Douglas fir-larch #1 | 9-11 | 13-1 | 16-5 | 19-1 | 9-8 | 12-4 | 15-0 | 17-5 |
| 40 psf · 16 in · Douglas fir-larch #2 | 9-9 | 12-9 | 15-7 | 18-1 | 9-3 | 11-8 | 14-3 | 16-6 |
| 40 psf · 16 in · Douglas fir-larch #3 | 7-8 | 9-9 | 11-11 | 13-10 | 7-0 | 8-11 | 10-11 | 12-7 |
| 40 psf · 16 in · Hem-fir SS | 9-9 | 12-10 | 16-5 | 19-11 | 9-9 | 12-10 | 16-5 | 19-11 |
| 40 psf · 16 in · Hem-fir #1 | 9-6 | 12-7 | 16-0 | 18-10 | 9-6 | 12-2 | 14-10 | 17-2 |
| 40 psf · 16 in · Hem-fir #2 | 9-1 | 12-0 | 15-2 | 17-7 | 8-11 | 11-4 | 13-10 | 16-1 |
| 40 psf · 16 in · Hem-fir #3 | 7-6 | 9-6 | 11-8 | 13-6 | 6-10 | 8-8 | 10-7 | 12-4 |
| 40 psf · 16 in · Southern pine SS | 10-2 | 13-4 | 17-0 | 20-9 | 10-2 | 13-4 | 17-0 | 20-9 |
| 40 psf · 16 in · Southern pine #1 | 9-9 | 12-10 | 16-1 | 19-1 | 9-9 | 12-7 | 14-8 | 17-5 |
| 40 psf · 16 in · Southern pine #2 | 9-4 | 11-10 | 14-0 | 16-6 | 8-6 | 10-10 | 12-10 | 15-1 |
| 40 psf · 16 in · Southern pine #3 | 7-1 | 8-11 | 10-10 | 12-10 | 6-5 | 8-2 | 9-10 | 11-8 |
| 40 psf · 16 in · Spruce-pine-fir SS | 9-6 | 12-7 | 16-0 | 19-6 | 9-6 | 12-7 | 16-0 | 19-6 |
| 40 psf · 16 in · Spruce-pine-fir #1 | 9-4 | 12-3 | 15-5 | 17-10 | 9-1 | 11-6 | 14-1 | 16-3 |
| 40 psf · 16 in · Spruce-pine-fir #2 | 9-4 | 12-3 | 15-5 | 17-10 | 9-1 | 11-6 | 14-1 | 16-3 |
| 40 psf · 16 in · Spruce-pine-fir #3 | 7-6 | 9-6 | 11-8 | 13-6 | 6-10 | 8-8 | 10-7 | 12-4 |
| 40 psf · 19.2 in · Douglas fir-larch SS | 9-8 | 12-10 | 16-4 | 19-10 | 9-8 | 12-10 | 16-4 | 19-6 |
| 40 psf · 19.2 in · Douglas fir-larch #1 | 9-4 | 12-4 | 15-0 | 17-5 | 8-10 | 11-3 | 13-8 | 15-11 |
| 40 psf · 19.2 in · Douglas fir-larch #2 | 9-2 | 11-8 | 14-3 | 16-6 | 8-5 | 10-8 | 13-0 | 15-1 |
| 40 psf · 19.2 in · Douglas fir-larch #3 | 7-0 | 8-11 | 10-11 | 12-7 | 6-5 | 8-2 | 9-11 | 11-6 |
| 40 psf · 19.2 in · Hem-fir SS | 9-2 | 12-1 | 15-5 | 18-9 | 9-2 | 12-1 | 15-5 | 18-9 |
| 40 psf · 19.2 in · Hem-fir #1 | 9-0 | 11-10 | 14-10 | 17-2 | 8-9 | 11-1 | 13-6 | 15-8 |
| 40 psf · 19.2 in · Hem-fir #2 | 8-7 | 11-3 | 13-10 | 16-1 | 8-2 | 10-4 | 12-8 | 14-8 |
| 40 psf · 19.2 in · Hem-fir #3 | 6-10 | 8-8 | 10-7 | 12-4 | 6-3 | 7-11 | 9-8 | 11-3 |
| 40 psf · 19.2 in · Southern pine SS | 9-6 | 12-7 | 16-0 | 19-6 | 9-6 | 12-7 | 16-0 | 19-6 |
| 40 psf · 19.2 in · Southern pine #1 | 9-2 | 12-1 | 14-8 | 17-5 | 9-0 | 11-5 | 13-5 | 15-11 |
| 40 psf · 19.2 in · Southern pine #2 | 8-6 | 10-10 | 12-10 | 15-1 | 7-9 | 9-10 | 11-8 | 13-9 |
| 40 psf · 19.2 in · Southern pine #3 | 6-5 | 8-2 | 9-10 | 11-8 | 5-11 | 7-5 | 9-0 | 10-8 |
| 40 psf · 19.2 in · Spruce-pine-fir SS | 9-0 | 11-10 | 15-1 | 18-4 | 9-0 | 11-10 | 15-1 | 17-9 |
| 40 psf · 19.2 in · Spruce-pine-fir #1 | 8-9 | 11-6 | 14-1 | 16-3 | 8-3 | 10-6 | 12-10 | 14-10 |
| 40 psf · 19.2 in · Spruce-pine-fir #2 | 8-9 | 11-6 | 14-1 | 16-3 | 8-3 | 10-6 | 12-10 | 14-10 |
| 40 psf · 19.2 in · Spruce-pine-fir #3 | 6-10 | 8-8 | 10-7 | 12-4 | 6-3 | 7-11 | 9-8 | 11-3 |
| 40 psf · 24 in · Douglas fir-larch SS | 9-0 | 11-11 | 15-2 | 18-5 | 9-0 | 11-11 | 15-0 | 17-5 |
| 40 psf · 24 in · Douglas fir-larch #1 | 8-8 | 11-0 | 13-5 | 15-7 | 7-11 | 10-0 | 12-3 | 14-3 |
| 40 psf · 24 in · Douglas fir-larch #2 | 8-3 | 10-5 | 12-9 | 14-9 | 7-6 | 9-6 | 11-8 | 13-6 |
| 40 psf · 24 in · Douglas fir-larch #3 | 6-3 | 8-0 | 9-9 | 11-3 | 5-9 | 7-3 | 8-11 | 10-4 |
| 40 psf · 24 in · Hem-fir SS | 8-6 | 11-3 | 14-4 | 17-5 | 8-6 | 11-3 | 14-4 | 16-10 |
| 40 psf · 24 in · Hem-fir #1 | 8-4 | 10-10 | 13-3 | 15-5 | 7-10 | 9-11 | 12-1 | 14-0 |
| 40 psf · 24 in · Hem-fir #2 | 7-11 | 10-2 | 12-5 | 14-4 | 7-4 | 9-3 | 11-4 | 13-1 |
| 40 psf · 24 in · Hem-fir #3 | 6-2 | 7-9 | 9-6 | 11-0 | 5-7 | 7-1 | 8-8 | 10-1 |
| 40 psf · 24 in · Southern pine SS | 8-10 | 11-8 | 14-11 | 18-1 | 8-10 | 11-8 | 14-11 | 18-0 |
| 40 psf · 24 in · Southern pine #1 | 8-6 | 11-3 | 13-1 | 15-7 | 8-1 | 10-3 | 12-0 | 14-3 |
| 40 psf · 24 in · Southern pine #2 | 7-7 | 9-8 | 11-5 | 13-6 | 7-0 | 8-10 | 10-5 | 12-4 |
| 40 psf · 24 in · Southern pine #3 | 5-9 | 7-3 | 8-10 | 10-5 | 5-3 | 6-8 | 8-1 | 9-6 |
| 40 psf · 24 in · Spruce-pine-fir SS | 8-4 | 11-0 | 14-0 | 17-0 | 8-4 | 11-0 | 13-8 | 15-11 |
| 40 psf · 24 in · Spruce-pine-fir #1 | 8-1 | 10-3 | 12-7 | 14-7 | 7-5 | 9-5 | 11-6 | 13-4 |
| 40 psf · 24 in · Spruce-pine-fir #2 | 8-1 | 10-3 | 12-7 | 14-7 | 7-5 | 9-5 | 11-6 | 13-4 |
| 40 psf · 24 in · Spruce-pine-fir #3 | 6-2 | 7-9 | 9-6 | 11-0 | 5-7 | 7-1 | 8-8 | 10-1 |
IRC 2021 Tables R502.3.1(1), sleeping areas at 30 psf live load, and R502.3.1(2), living areas at 40 psf, as printed: feet-inches (15-7 is 15 ft 7 in). L/Δ = 360. Check sources for availability of lumber in lengths greater than 20 feet. End bearing length shall be increased to 2 inches (Table R502.3.1(2), note a, on the Hem-fir SS row at 24 in on center).
Where the numbers come from
- Spans: 2021 International Residential Code, Section R502.3.1 and Tables R502.3.1(1), Floor Joist Spans for Common Lumber Species in residential sleeping areas at a 30 psf live load, and R502.3.1(2), the same for living areas at 40 psf, printed in full below. Both limit deflection to L/360 and give each span for a 10 psf and a 20 psf dead load. Read October 17, 2026, in the code text published by UpCodes, checked cell by cell against the model text reproduced in the 2021 Seattle Residential Code, and read again October 18, 2026. Read the code
- Nothing here is calculated: the page looks up the cell for your species, grade, size, spacing and loads, and for a span you type it lists the sizes whose cell is at least that long.
These are the IRC's tables for sawn lumber in a house. I-joists and engineered lumber carry their maker's own span tables, and a floor under a hot tub, a piano or a heavy wall is an engineered load. Your state or county adopts a version of the IRC and can amend the tables: the span your inspector accepts is the one in your adopted code.
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