Deck beam span calculator: how far can a deck beam span between posts?
9 ft 0 in
maximum beam span, 2-ply 2 × 10 · effective joist span 12 × 0.66 = 7.92 ft, read in the 8 ft column · for 2-ply 2 × 10 Southern pine, 12 ft joists, IRC R507.5
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
9 ft 0 in
maximum beam span, 2-ply 2 × 10 · effective joist span 12 × 0.66 = 7.92 ft, read in the 8 ft column
Source: IRC 2021 Tables R507.5(1) to R507.5(5), Maximum Deck Beam Span and Joist Span Factors (International Code Council), read October 17, 2026. Read the source
A 2-ply 2 × 10 Southern pine deck beam carrying 12 ft joists with no overhang can span 9 ft 0 in between posts under a 40 psf live load (IRC 2021 Table R507.5(1), at 7.92 ft of effective joist span).
A worked example
A 3-ply 2 × 12 hem-fir beam under 13 ft joists that overhang it by 2 ft, with a 60 psf ground snow load needs 9 ft 4 in. The overhang is 2 ÷ 13 = 0.15 of the joist span, which takes the 1/6 row of Table R507.5(5), factor 0.90: 13 × 0.90 = 11.7 ft of effective joist span, read in the 12 ft column of Table R507.5(3).
How far can a 2x10 deck beam span?
It depends on the joists it carries, because the IRC reads the beam span against the effective joist span. A 2-ply 2 × 10 Southern pine beam under 12 ft joists with no overhang spans 9 ft 0 in at a 40 psf live load; a 3-ply 2 × 10 under the same joists spans 11 ft 2 in, and a single 2 × 10 spans 6 ft 0 in. Under 8 ft joists the 2-ply beam reaches 10 ft 4 in.
What is the effective joist span?
The joist span multiplied by a factor from IRC Table R507.5(5) that grows with the joist overhang past the beam: 0.66 with no overhang, 0.72 at 1/12 of the span, 0.80 at 1/10, 0.84 at 1/8, 0.90 at 1/6 and 1.00 at 1/4. An overhang loads the beam more, so the same beam spans less. The table prints the 1/12 row as “1/12 (0.87)”; 1/12 is 0.083, and the factor on that row is 0.72.
What else it is called
A deck beam span calculator is also searched as a deck beam span chart, deck beam span between posts or “how far can a 2x10 deck beam span”. A 2-ply beam is two boards nailed together face to face; the IRC table counts plies, so a doubled 2 × 10 is a 2-ply 2 × 10.
The full IRC table
| Load · species · beam | 6 ft effective joist span | 8 ft effective joist span | 10 ft effective joist span | 12 ft effective joist span | 14 ft effective joist span | 16 ft effective joist span | 18 ft effective joist span |
|---|---|---|---|---|---|---|---|
| 40 psf live · Southern pine · 1-ply 2 × 6 | 4-7 | 4-0 | 3-7 | 3-3 | 3-0 | 2-10 | 2-8 |
| 40 psf live · Southern pine · 1-ply 2 × 8 | 5-11 | 5-1 | 4-7 | 4-2 | 3-10 | 3-7 | 3-5 |
| 40 psf live · Southern pine · 1-ply 2 × 10 | 7-0 | 6-0 | 5-5 | 4-11 | 4-7 | 4-3 | 4-0 |
| 40 psf live · Southern pine · 1-ply 2 × 12 | 8-3 | 7-1 | 6-4 | 5-10 | 5-5 | 5-0 | 4-9 |
| 40 psf live · Southern pine · 2-ply 2 × 6 | 6-11 | 5-11 | 5-4 | 4-10 | 4-6 | 4-3 | 4-0 |
| 40 psf live · Southern pine · 2-ply 2 × 8 | 8-9 | 7-7 | 6-9 | 6-2 | 5-9 | 5-4 | 5-0 |
| 40 psf live · Southern pine · 2-ply 2 × 10 | 10-4 | 9-0 | 8-0 | 7-4 | 6-9 | 6-4 | 6-0 |
| 40 psf live · Southern pine · 2-ply 2 × 12 | 12-2 | 10-7 | 9-5 | 8-7 | 8-0 | 7-5 | 7-0 |
| 40 psf live · Southern pine · 3-ply 2 × 6 | 8-6 | 7-5 | 6-8 | 6-1 | 5-8 | 5-3 | 4-11 |
| 40 psf live · Southern pine · 3-ply 2 × 8 | 10-11 | 9-6 | 8-6 | 7-9 | 7-2 | 6-8 | 6-4 |
| 40 psf live · Southern pine · 3-ply 2 × 10 | 13-0 | 11-2 | 10-0 | 9-2 | 8-6 | 7-11 | 7-6 |
| 40 psf live · Southern pine · 3-ply 2 × 12 | 15-3 | 13-3 | 11-10 | 10-9 | 10-0 | 9-4 | 8-10 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 6 | 4-1 | 3-6 | 3-0 | 2-8 | 2-5 | 2-3 | 2-1 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 8 | 5-6 | 4-8 | 4-0 | 3-6 | 3-2 | 2-11 | 2-9 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 10 | 6-8 | 5-10 | 5-1 | 4-6 | 4-1 | 3-9 | 3-6 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 12 | 7-9 | 6-9 | 6-0 | 5-6 | 5-0 | 3-9 | 3-6 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 6 | 6-1 | 5-3 | 4-9 | 4-4 | 3-11 | 3-7 | 3-3 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 8 | 8-2 | 7-1 | 6-4 | 5-9 | 5-2 | 4-8 | 4-4 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 10 | 10-0 | 8-7 | 7-9 | 7-0 | 6-6 | 6-0 | 5-6 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 12 | 11-7 | 10-0 | 8-11 | 8-2 | 7-7 | 7-1 | 6-8 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 6 | 7-8 | 6-8 | 6-0 | 5-6 | 5-1 | 4-9 | 4-6 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 8 | 10-3 | 8-10 | 7-11 | 7-3 | 6-8 | 6-3 | 5-11 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 10 | 12-6 | 10-10 | 9-8 | 8-10 | 8-2 | 7-8 | 7-2 |
| 40 psf live · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 12 | 14-6 | 12-7 | 11-3 | 10-3 | 9-6 | 8-11 | 8-5 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 6 | 4-2 | 3-7 | 3-1 | 2-9 | 2-6 | 2-3 | 2-2 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 8 | 5-4 | 4-7 | 4-1 | 3-7 | 3-3 | 3-0 | 2-10 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 10 | 6-6 | 5-7 | 5-0 | 4-7 | 4-2 | 3-10 | 3-7 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 12 | 7-6 | 6-6 | 5-10 | 5-4 | 4-11 | 4-7 | 4-4 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 6 | 6-2 | 5-4 | 4-10 | 4-5 | 4-0 | 3-8 | 3-4 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 8 | 7-10 | 6-10 | 6-1 | 5-7 | 5-2 | 4-10 | 4-5 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 10 | 9-7 | 8-4 | 7-5 | 6-9 | 6-3 | 5-10 | 5-6 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 12 | 11-1 | 9-8 | 8-7 | 7-10 | 7-3 | 6-10 | 6-5 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 6 | 7-8 | 6-9 | 6-0 | 5-6 | 5-1 | 4-9 | 4-6 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 8 | 9-10 | 8-6 | 7-7 | 6-11 | 6-5 | 6-0 | 5-8 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 10 | 12-0 | 10-5 | 9-4 | 8-6 | 7-10 | 7-4 | 6-11 |
| 40 psf live · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 12 | 13-11 | 12-1 | 10-9 | 9-10 | 9-1 | 8-6 | 8-1 |
| 50 psf snow · Southern pine · 1-ply 2 × 6 | 4-6 | 3-11 | 3-6 | 3-2 | 2-11 | 2-9 | 2-7 |
| 50 psf snow · Southern pine · 1-ply 2 × 8 | 5-9 | 4-11 | 4-5 | 4-0 | 3-9 | 3-6 | 3-3 |
| 50 psf snow · Southern pine · 1-ply 2 × 10 | 6-9 | 5-10 | 5-3 | 4-9 | 4-5 | 4-2 | 3-11 |
| 50 psf snow · Southern pine · 1-ply 2 × 12 | 8-0 | 6-11 | 6-2 | 5-8 | 5-3 | 4-11 | 4-7 |
| 50 psf snow · Southern pine · 2-ply 2 × 6 | 6-8 | 5-9 | 5-2 | 4-9 | 4-4 | 4-1 | 3-10 |
| 50 psf snow · Southern pine · 2-ply 2 × 8 | 8-6 | 7-4 | 6-7 | 6-0 | 5-7 | 5-2 | 4-11 |
| 50 psf snow · Southern pine · 2-ply 2 × 10 | 10-1 | 8-9 | 7-10 | 7-1 | 6-7 | 6-2 | 5-10 |
| 50 psf snow · Southern pine · 2-ply 2 × 12 | 11-11 | 10-3 | 9-2 | 8-5 | 7-9 | 7-3 | 6-10 |
| 50 psf snow · Southern pine · 3-ply 2 × 6 | 7-11 | 7-2 | 6-6 | 5-11 | 5-6 | 5-1 | 4-10 |
| 50 psf snow · Southern pine · 3-ply 2 × 8 | 10-5 | 9-3 | 8-3 | 7-6 | 6-11 | 6-6 | 6-2 |
| 50 psf snow · Southern pine · 3-ply 2 × 10 | 12-8 | 10-11 | 9-9 | 8-11 | 8-3 | 7-9 | 7-3 |
| 50 psf snow · Southern pine · 3-ply 2 × 12 | 14-11 | 12-11 | 11-6 | 10-6 | 9-9 | 9-1 | 8-7 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 6 | 4-0 | 3-5 | 2-11 | 2-7 | 2-4 | 2-2 | 2-0 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 8 | 5-4 | 4-7 | 3-11 | 3-5 | 3-1 | 2-10 | 2-8 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 10 | 6-7 | 5-8 | 4-11 | 4-5 | 4-0 | 3-8 | 3-5 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 12 | 7-7 | 6-7 | 5-11 | 5-4 | 4-10 | 4-6 | 4-2 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 6 | 6-0 | 5-2 | 4-7 | 4-2 | 3-10 | 3-5 | 3-2 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 8 | 8-0 | 6-11 | 6-2 | 5-8 | 5-0 | 4-7 | 4-2 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 10 | 9-9 | 8-5 | 7-7 | 6-11 | 6-4 | 5-10 | 5-4 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 12 | 11-4 | 9-10 | 8-9 | 8-0 | 7-5 | 6-11 | 6-6 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 6 | 7-6 | 6-6 | 5-9 | 5-3 | 4-11 | 4-7 | 4-4 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 8 | 10-0 | 8-8 | 7-9 | 7-1 | 6-6 | 6-1 | 5-8 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 10 | 12-3 | 10-7 | 9-6 | 8-8 | 8-0 | 7-6 | 7-0 |
| 50 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 12 | 14-3 | 12-4 | 11-0 | 10-1 | 9-4 | 8-9 | 8-3 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 6 | 4-1 | 3-6 | 3-0 | 2-8 | 2-5 | 2-3 | 2-1 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 8 | 5-2 | 4-6 | 4-0 | 3-6 | 3-2 | 2-11 | 2-9 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 10 | 6-4 | 5-6 | 4-11 | 4-6 | 4-1 | 3-9 | 3-6 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 12 | 7-4 | 6-4 | 5-8 | 5-2 | 4-10 | 4-6 | 4-3 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 6 | 6-1 | 5-3 | 4-8 | 4-4 | 3-11 | 3-6 | 3-3 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 8 | 7-8 | 6-8 | 5-11 | 5-5 | 5-0 | 4-8 | 4-3 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 10 | 9-5 | 8-2 | 7-3 | 6-8 | 6-2 | 5-9 | 5-5 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 12 | 10-11 | 9-5 | 8-5 | 7-8 | 7-2 | 6-8 | 6-3 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 6 | 7-1 | 6-5 | 5-11 | 5-5 | 5-0 | 4-8 | 4-5 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 8 | 9-4 | 8-4 | 7-5 | 6-10 | 604 | 5-11 | 5-7 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 10 | 11-9 | 10-2 | 9-1 | 8-4 | 7-8 | 7-2 | 6-9 |
| 50 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 12 | 13-8 | 11-10 | 10-7 | 9-8 | 8-11 | 8-4 | 7-10 |
| 60 psf snow · Southern pine · 1-ply 2 × 6 | 4-2 | 3-7 | 3-3 | 2-11 | 2-9 | 2-6 | 2-5 |
| 60 psf snow · Southern pine · 1-ply 2 × 8 | 5-3 | 4-7 | 4-1 | 3-9 | 3-5 | 3-3 | 3-0 |
| 60 psf snow · Southern pine · 1-ply 2 × 10 | 6-3 | 5-5 | 4-10 | 4-5 | 4-1 | 3-10 | 3-7 |
| 60 psf snow · Southern pine · 1-ply 2 × 12 | 7-5 | 6-5 | 5-9 | 5-3 | 4-10 | 4-6 | 4-3 |
| 60 psf snow · Southern pine · 2-ply 2 × 6 | 6-2 | 5-4 | 4-9 | 4-4 | 4-0 | 3-9 | 3-7 |
| 60 psf snow · Southern pine · 2-ply 2 × 8 | 7-10 | 6-10 | 6-1 | 5-7 | 5-2 | 4-10 | 4-6 |
| 60 psf snow · Southern pine · 2-ply 2 × 10 | 9-4 | 8-1 | 7-3 | 6-7 | 6-1 | 5-8 | 5-4 |
| 60 psf snow · Southern pine · 2-ply 2 × 12 | 11-0 | 9-6 | 8-6 | 7-9 | 7-2 | 6-9 | 6-4 |
| 60 psf snow · Southern pine · 3-ply 2 × 6 | 7-5 | 6-9 | 6-0 | 5-6 | 5-1 | 4-9 | 4-6 |
| 60 psf snow · Southern pine · 3-ply 2 × 8 | 9-9 | 8-6 | 7-8 | 6-11 | 6-5 | 6-0 | 5-8 |
| 60 psf snow · Southern pine · 3-ply 2 × 10 | 11-8 | 10-2 | 9-1 | 8-3 | 7-8 | 7-2 | 6-9 |
| 60 psf snow · Southern pine · 3-ply 2 × 12 | 13-9 | 11-11 | 10-8 | 9-9 | 9-0 | 8-5 | 7-11 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 6 | 3-8 | 3-1 | 2-8 | 2-4 | 2-2 | 2-0 | 1-10 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 8 | 5-0 | 4-1 | 3-6 | 3-1 | 2-10 | 2-7 | 2-5 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 10 | 6-1 | 5-2 | 4-6 | 4-0 | 3-7 | 3-4 | 3-2 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 12 | 7-1 | 6-1 | 5-5 | 4-10 | 4-5 | 4-1 | 3-10 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 6 | 5-6 | 4-9 | 4-3 | 3-10 | 3-5 | 3-1 | 2-10 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 8 | 7-5 | 6-5 | 5-9 | 5-0 | 4-6 | 4-1 | 3-9 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 10 | 9-0 | 7-10 | 7-0 | 6-4 | 5-9 | 5-2 | 4-10 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 12 | 10-6 | 9-1 | 8-1 | 7-5 | 6-10 | 6-4 | 5-10 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 6 | 6-11 | 6-0 | 5-4 | 4-11 | 4-6 | 4-2 | 3-10 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 8 | 9-3 | 8-0 | 7-2 | 6-6 | 6-1 | 5-6 | 5-0 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 10 | 11-4 | 9-10 | 8-9 | 8-0 | 7-5 | 6-11 | 6-5 |
| 60 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 12 | 13-2 | 11-5 | 10-2 | 9-4 | 8-7 | 8-1 | 7-7 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 6 | 3-9 | 3-2 | 2-9 | 2-5 | 2-2 | 2-0 | 1-11 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 8 | 4-10 | 4-2 | 3-7 | 3-2 | 2-11 | 2-8 | 2-6 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 10 | 5-10 | 5-1 | 4-6 | 4-1 | 3-8 | 3-5 | 3-3 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 12 | 6-10 | 5-11 | 5-3 | 4-10 | 4-5 | 4-2 | 3-11 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 6 | 5-7 | 4-10 | 4-4 | 3-11 | 3-6 | 3-2 | 2-11 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 8 | 7-1 | 6-2 | 5-6 | 5-0 | 4-7 | 4-2 | 3-10 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 10 | 8-8 | 7-6 | 6-9 | 6-2 | 5-8 | 5-4 | 4-11 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 12 | 10-1 | 8-9 | 7-10 | 7-2 | 6-7 | 6-2 | 5-10 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 6 | 6-8 | 6-1 | 5-5 | 5-0 | 4-7 | 4-3 | 3-11 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 8 | 8-9 | 7-9 | 6-22 | 6-4 | 5-20 | 5-5 | 5-3 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 10 | 10-11 | 9-5 | 8-5 | 7-8 | 7-3 | 6-8 | 6-3 |
| 60 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 12 | 12-8 | 10-11 | 9-9 | 8-11 | 8-3 | 7-9 | 7-3 |
| 70 psf snow · Southern pine · 1-ply 2 × 6 | 3-11 | 3-4 | 3-0 | 2-9 | 2-6 | 2-4 | 2-3 |
| 70 psf snow · Southern pine · 1-ply 2 × 8 | 4-11 | 4-3 | 3-10 | 3-6 | 3-3 | 3-0 | 2-10 |
| 70 psf snow · Southern pine · 1-ply 2 × 10 | 5-10 | 5-1 | 4-6 | 4-2 | 3-10 | 3-7 | 3-4 |
| 70 psf snow · Southern pine · 1-ply 2 × 12 | 6-11 | 6-0 | 5-4 | 4-11 | 4-6 | 4-3 | 4-0 |
| 70 psf snow · Southern pine · 2-ply 2 × 6 | 5-9 | 5-0 | 4-6 | 4-1 | 3-9 | 3-6 | 3-4 |
| 70 psf snow · Southern pine · 2-ply 2 × 8 | 7-4 | 6-4 | 5-8 | 5-2 | 4-10 | 4-6 | 4-3 |
| 70 psf snow · Southern pine · 2-ply 2 × 10 | 8-9 | 7-7 | 6-9 | 6-2 | 5-8 | 5-4 | 5-0 |
| 70 psf snow · Southern pine · 2-ply 2 × 12 | 10-3 | 8-11 | 8-0 | 7-3 | 6-9 | 6-3 | 5-11 |
| 70 psf snow · Southern pine · 3-ply 2 × 6 | 7-0 | 6-3 | 5-7 | 5-1 | 4-9 | 4-5 | 4-2 |
| 70 psf snow · Southern pine · 3-ply 2 × 8 | 9-3 | 8-0 | 7-2 | 6-6 | 6-0 | 5-8 | 5-4 |
| 70 psf snow · Southern pine · 3-ply 2 × 10 | 10-11 | 9-6 | 8-6 | 7-9 | 7-2 | 6-8 | 6-4 |
| 70 psf snow · Southern pine · 3-ply 2 × 12 | 12-11 | 11-2 | 10-0 | 9-1 | 8-5 | 7-11 | 7-5 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 6 | 3-5 | 2-10 | 2-5 | 2-2 | 2-0 | 1-10 | 1-9 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 8 | 4-7 | 3-8 | 3-2 | 2-10 | 2-7 | 2-5 | 2-4 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 10 | 5-8 | 4-9 | 4-1 | 3-8 | 3-4 | 3-1 | 2-11 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 1-ply 2 × 12 | 6-7 | 5-8 | 5-0 | 4-6 | 4-1 | 3-10 | 3-7 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 6 | 5-2 | 4-6 | 4-0 | 3-5 | 3-1 | 2-10 | 2-7 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 8 | 6-11 | 6-0 | 5-3 | 4-7 | 4-1 | 3-8 | 3-5 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 10 | 8-5 | 7-4 | 6-6 | 5-10 | 5-2 | 4-9 | 4-5 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 2-ply 2 × 12 | 9-10 | 8-6 | 7-7 | 6-11 | 6-4 | 5-9 | 5-4 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 6 | 6-6 | 5-7 | 5-0 | 4-7 | 4-2 | 3-9 | 3-5 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 8 | 8-8 | 7-6 | 6-8 | 6-1 | 5-6 | 5-0 | 4-7 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 10 | 10-7 | 9-2 | 8-2 | 7-6 | 6-11 | 6-4 | 5-10 |
| 70 psf snow · Douglas fir-larch, hem-fir, spruce-pine-fir · 3-ply 2 × 12 | 12-4 | 10-8 | 9-7 | 8-9 | 8-1 | 7-7 | 7-1 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 6 | 3-6 | 2-11 | 2-6 | 2-3 | 2-0 | 1-11 | 1-9 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 8 | 4-6 | 3-10 | 3-3 | 2-11 | 2-8 | 2-6 | 2-4 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 10 | 5-6 | 4-9 | 4-2 | 3-9 | 3-5 | 3-2 | 3-0 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 1-ply 2 × 12 | 6-4 | 5-6 | 4-11 | 4-6 | 4-2 | 3-11 | 3-8 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 6 | 5-3 | 4-7 | 4-1 | 3-6 | 3-2 | 2-11 | 2-8 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 8 | 6-8 | 5-9 | 5-2 | 4-8 | 4-2 | 3-10 | 3-6 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 10 | 8-2 | 7-1 | 6-4 | 5-9 | 5-4 | 4-10 | 4-6 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 2-ply 2 × 12 | 9-5 | 8-2 | 7-4 | 6-8 | 6-2 | 5-9 | 5-5 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 6 | 6-4 | 5-8 | 5-1 | 4-8 | 4-3 | 3-10 | 3-6 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 8 | 8-4 | 7-3 | 6-5 | 5-11 | 5-5 | 5-1 | 4-8 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 10 | 10-2 | 8-10 | 7-11 | 7-2 | 6-8 | 6-3 | 5-11 |
| 70 psf snow · Redwood, western cedars, ponderosa pine, red pine · 3-ply 2 × 12 | 11-10 | 10-3 | 9-2 | 8-4 | 7-9 | 7-3 | 6-10 |
IRC 2021 Tables R507.5(1) to R507.5(4), Maximum Deck Beam Span, as printed: feet-inches (9-0 is 9 ft 0 in). Effective joist span = actual joist span × the Table R507.5(5) factor for overhang ÷ span: 0 (no cantilever) → 0.66; 1/12 (0.87) → 0.72; 1/10 (0.10) → 0.80; 1/8 (0.125) → 0.84; 1/6 (0.167) → 0.90; 1/4 (0.250) → 1.00. Interpolation permitted. Extrapolation not permitted. Dead load = 10 psf, L/Δ = 360 at main span, L/Δ = 180 at cantilever. Snow load is not assumed to be concurrent with live load. No. 2 grade, wet service factor included. Beam cantilevers are limited to the adjacent beam's span divided by 4. Three redwood 3-ply 2 × 8 cells are printed as “604” (50 psf, 14 ft) and “6-22” and “5-20” (60 psf, 10 and 14 ft), which are not spans; the calculator skips them.
Where the numbers come from
- Beam spans: 2021 International Residential Code, Section R507.5 and Tables R507.5(1) to R507.5(4), Maximum Deck Beam Span, for a 40 psf live load and 50, 60 and 70 psf ground snow loads, printed in full below, and Table R507.5(5), Joist Span Factors for Calculating Effective Deck Joist Span. They assume No. 2 grade lumber with the wet service factor, a 10 psf dead load and deflection limited to L/360, allow interpolation but not extrapolation, and limit a beam's overhang past its post to a quarter of the adjacent span. 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
- The page multiplies your joist span by the factor for your overhang, rounding the overhang up to the next row of Table R507.5(5) and the result up to the next column of the beam table, so it never gives a longer span than interpolating would. Three cells for 3-ply 2 × 8 redwood are printed in the 2021 IRC as “604”, “6-22” and “5-20”, which are not spans: the calculator skips them, uses the next column and says so.
The beam span is the distance between posts. A beam can run past its end post by at most a quarter of that span, and its depth must be at least the joists' depth where they hang flush from it. Glulam and LVL beams carry their maker's tables, and a hot tub or a roof over the deck is an engineered load. Your state or county adopts a version of the IRC and can amend the tables.
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