Deck Beam Span Calculator
A southern pine 2-2x10 deck beam, with joists up to 10 feet, spans 7'-9" on DCA 6 Table 3A. LB/4 of that cell is 1'-11.25".
Beam cells confirmed on the DCA 6 file published by the American Wood Council. The opening row is Table 3A, southern pine, 2-2x10, joists ≤ 10 ft. The 0.89 box appears only for glulam.
A deck beam span calculator with the deck beam span chart from Tables 3A and 3B. Dimension lumber is 3A. Glued laminated timber is 3B.
The joist that sets which column you need: deck joist span calculator. Boards and fasteners after the frame is sized: deck calculator.
Deck beam span
Pick the column that is at least as long as the joist span. A 9 ft joist uses the 10 ft column. The table does not interpolate. Joists are assumed on one side of the beam. This is a deck beam table, not an interior floor beam.
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Table 3A, dimension lumber
Source: American Wood Council DCA 6, based on the 2015 IRC. Table 3A is on guide page 6. The title is “Dimension Lumber Deck Beam Spans (LB) Supporting a Single Span of Joists with or without Overhangs.” Footnote 1 assumes 40 psf live load, 10 psf dead load, an L/360 simple-span deflection limit, a cantilever length/180 deflection limit, No. 2 grade, and wet service. Footnote 4 says beam depth must be at least the joist depth when joist hangers are used.
Southern pine is its own block. The second block is one combined line: Douglas fir-larch together with hem-fir and with spruce-pine-fir, followed by redwood, then the western cedars, ponderosa pine, and red pine. Footnote 2 applies incising to Douglas fir-larch, to hem-fir, and to spruce-pine-fir. Footnote 3 uses northern-species values, without incising, for ponderosa pine and for red pine. The guide prints one span for the whole block, so this chart does not split it.
Southern Pine
| Beam | ≤ 6' | ≤ 8' | ≤ 10' | ≤ 12' | ≤ 14' | ≤ 16' | ≤ 18' |
|---|---|---|---|---|---|---|---|
| 2-2x6 | 6'-8" | 5'-8" | 5'-1" | 4'-7" | 4'-3" | 4'-0" | 3'-9" |
| 2-2x8 | 8'-6" | 7'-4" | 6'-6" | 5'-11" | 5'-6" | 5'-1" | 4'-9" |
| 2-2x10 | 10'-1" | 8'-9" | 7'-9" | 7'-1" | 6'-6" | 6'-1" | 5'-9" |
| 2-2x12 | 11'-11" | 10'-4" | 9'-2" | 8'-4" | 7'-9" | 7'-3" | 6'-9" |
| 3-2x6 | 7'-11" | 7'-2" | 6'-5" | 5'-10" | 5'-5" | 5'-0" | 4'-9" |
| 3-2x8 | 10'-7" | 9'-3" | 8'-3" | 7'-6" | 6'-11" | 6'-5" | 6'-1" |
| 3-2x10 | 12'-9" | 11'-0" | 9'-9" | 8'-9" | 8'-3" | 7'-8" | 7'-3" |
| 3-2x12 | 15'-0" | 13'-0" | 11'-7" | 10'-6" | 9'-9" | 9'-1" | 8'-7" |
Douglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir, Redwood, Western Cedars, Ponderosa Pine, Red Pine
| Beam | ≤ 6' | ≤ 8' | ≤ 10' | ≤ 12' | ≤ 14' | ≤ 16' | ≤ 18' |
|---|---|---|---|---|---|---|---|
| 3x6 or 2-2x6 | 5'-2" | 4'-5" | 3'-11" | 3'-7" | 3'-3" | 2'-10" | 2'-6" |
| 3x8 or 2-2x8 | 6'-7" | 5'-8" | 5'-1" | 4'-7" | 4'-3" | 3'-10" | 3'-5" |
| 3x10 or 2-2x10 | 8'-1" | 7'-0" | 6'-3" | 5'-8" | 5'-3" | 4'-10" | 4'-5" |
| 3x12 or 2-2x12 | 9'-5" | 8'-2" | 7'-3" | 6'-7" | 6'-1" | 5'-8" | 5'-4" |
| 4x6 | 6'-2" | 5'-3" | 4'-8" | 4'-3" | 3'-11" | 3'-8" | 3'-5" |
| 4x8 | 8'-2" | 7'-0" | 6'-3" | 5'-8" | 5'-3" | 4'-11" | 4'-7" |
| 4x10 | 9'-8" | 8'-4" | 7'-5" | 6'-9" | 6'-3" | 5'-10" | 5'-5" |
| 4x12 | 11'-2" | 9'-8" | 8'-7" | 7'-10" | 7'-3" | 6'-9" | 6'-4" |
| 3-2x6 | 7'-1" | 6'-5" | 5'-9" | 5'-3" | 4'-10" | 4'-6" | 4'-3" |
| 3-2x8 | 9'-5" | 8'-3" | 7'-4" | 6'-8" | 6'-2" | 5'-9" | 5'-5" |
| 3-2x10 | 11'-9" | 10'-2" | 9'-1" | 8'-3" | 7'-7" | 7'-1" | 6'-8" |
| 3-2x12 | 13'-8" | 11'-10" | 10'-6" | 9'-7" | 8'-10" | 8'-3" | 7'-10" |
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Table 3B, glued laminated timber
Table 3B is on guide page 7. Footnote 1 repeats the load and deflection basis, requires a naturally durable species or AWPA U1 treatment, and says spans for beams not treated with oil-borne preservatives are multiplied by 0.89. Footnote 5 caps a cell at 18'-0" for footing design. Those capped cells are marked below. The 0.89 box multiplies the printed inches, including a capped 18'-0" cell, and LB/4 then uses that product.
Balanced or Unbalanced 20F-1.5E and higher grade Cedar
| Width × depth | ≤ 6' | ≤ 8' | ≤ 10' | ≤ 12' | ≤ 14' | ≤ 16' | ≤ 18' |
|---|---|---|---|---|---|---|---|
| 3-1/2" × 9-1/2" | 12'-2" | 10'-6" | 9'-4" | 8'-6" | 7'-10" | 7'-4" | 6'-11" |
| 3-1/2" × 11-7/8" | 15'-2" | 13'-1" | 11'-8" | 10'-8" | 9'-10" | 9'-2" | 8'-8" |
| 3-1/2" × 14" | 17'-10" | 15'-5" | 13'-9" | 12'-7" | 11'-7" | 10'-10" | 10'-2" |
| 5-1/4" × 11-7/8" | 18'-0" (note 5) | 16'-8" | 14'-10" | 13'-7" | 12'-6" | 11'-8" | 11'-0" |
| 5-1/4" × 14" | 18'-0" (note 5) | 18'-0" (note 5) | 17'-6" | 15'-11" | 14'-9" | 13'-9" | 13'-0" |
| 5-1/4" × 16" | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 16'-10" | 15'-9" | 14'-10" |
Unbalanced 24F-1.8E Douglas Fir-Larch or Southern Pine
| Width × depth | ≤ 6' | ≤ 8' | ≤ 10' | ≤ 12' | ≤ 14' | ≤ 16' | ≤ 18' |
|---|---|---|---|---|---|---|---|
| 3-1/2" × 9-1/2" | 13'-11" | 12'-1" | 10'-9" | 9'-10" | 9'-1" | 8'-6" | 8'-0" |
| 3-1/2" × 11-7/8" | 17'-5" | 15'-1" | 13'-5" | 12'-3" | 11'-4" | 10'-7" | 10'-0" |
| 3-1/2" × 14" | 18'-0" (note 5) | 17'-9" | 15'-10" | 14'-5" | 13'-4" | 12'-6" | 11'-9" |
| 5-1/4" × 11-7/8" | 18'-0" (note 5) | 18'-0" (note 5) | 17'-1" | 15'-7" | 14'-5" | 13'-6" | 12'-8" |
| 5-1/4" × 14" | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 17'-0" | 15'-10" | 14'-11" |
| 5-1/4" × 16" | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 17'-0" |
Balanced 24F-1.8E Douglas Fir-Larch or Southern Pine
| Width × depth | ≤ 6' | ≤ 8' | ≤ 10' | ≤ 12' | ≤ 14' | ≤ 16' | ≤ 18' |
|---|---|---|---|---|---|---|---|
| 3-1/2" × 9-1/2" | 13'-11" | 12'-7" | 11'-8" | 11'-0" | 10'-5" | 9'-11" | 9'-7" |
| 3-1/2" × 11-7/8" | 17'-5" | 15'-10" | 14'-8" | 13'-9" | 13'-1" | 12'-6" | 12'-0" |
| 3-1/2" × 14" | 18'-0" (note 5) | 18'-0" (note 5) | 17'-4" | 16'-3" | 15'-5" | 14'-9" | 14'-2" |
| 5-1/4" × 11-7/8" | 18'-0" (note 5) | 18'-0" (note 5) | 17'-4" | 16'-3" | 15'-5" | 14'-9" | 14'-2" |
| 5-1/4" × 14" | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 17'-6" | 16'-9" |
| 5-1/4" × 16" | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) | 18'-0" (note 5) |
Worked lookups
- Southern pine 2-2x10, joists ≤ 10 ft: 7'-9". 7 × 12 + 9 = 93 inches. 93 ÷ 4 = 23.25 inches, printed 1'-11.25".
- Combined species group, 3-2x8, joists ≤ 8 ft: 8'-3". 99 ÷ 4 = 24.75 inches, printed 2'-0.75".
- Unbalanced 24F-1.8E, 3-1/2 in by 11-7/8 in, joists ≤ 8 ft: printed 15'-1". 181 × 0.89 = 161.09 inches, which is 13'-5.09". That reduced length ÷ 4 is 3'-4.27".
Deck beam questions
What beam span does southern pine 2-2x10 get at a 10 foot joist column?
Leave the group on Table 3A Southern Pine, the size on 2-2x10, and the column on Joists ≤ 10 ft. Printed beam span reads 7'-9". Span × 0.89 reads Off. The line above is the printed cell. Past the post, LB/4 reads 1'-11.25".
What does the combined species group list for a triple 2x8 at 8 feet?
Choose Table 3A for Douglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir, Redwood, Western Cedars, Ponderosa Pine, Red Pine. Set the size to 3-2x8 and the column to Joists ≤ 8 ft. Printed beam span reads 8'-3". Past the post, LB/4 reads 2'-0.75".
What is 15 feet 1 inch times 0.89?
Choose Table 3B, Unbalanced 24F-1.8E Douglas Fir-Larch or Southern Pine, size 3-1/2" × 11-7/8", column Joists ≤ 8 ft. With the 0.89 box off, printed beam span reads 15'-1" and LB/4 reads 3'-9.25". Turn the box on. Printed beam span stays 15'-1". Span × 0.89 reads 13'-5.09". Past the post, LB/4 reads 3'-4.27", because the quarter then uses the reduced span.
Why is there no 9 foot column?
The headers are joist spans less than or equal to 6, 8, 10, 12, 14, 16, and 18 feet. A joist that is longer than 8 feet and not longer than 10 feet uses the 10 foot column. The panel does not invent a span between columns.
May the joists bear on both sides of this beam?
The beam section says joists shall not frame in from opposite sides of the same beam. The commentary says that equal joists on opposite sides can use the column for twice the joist span: 8 foot joists each side would use the 16 foot column. This page does not switch columns for you. If that case applies, pick the doubled column yourself.
Is the post extension measured from the face or the center?
The beam-size section says the beam can extend past the post face up to LB/4, as Figure 3 shows. The commentary says past the post centerline up to LB/4. Both sentences are in the same guide. The panel reports LB/4 of the span it is using and does not choose a measuring point the guide states two ways.