Deck span tables

The joist, beam and post tables from the AWC Prescriptive Residential Wood Deck Construction Guide, laid out by species and spacing, with a calculator on top to find your row.

At 10'-0" and 16 in on center in Southern Pine, the smallest joist DCA 6 allows is a 2x8. It spans up to 11'-10" and may overhang the beam by up to 2'-0".

Table 2 for Southern Pine, 40 psf live and 10 psf dead load, No. 2 grade, wet service. Your row is highlighted.

Allowable joist span and overhang, DCA 6 Table 2
Joist	Span 12 in	Span 16 in	Span 24 in	Overhang 12 in	Overhang 16 in	Overhang 24 in
2x6	9'-11"	9'-0"	7'-7"	1'-0"	1'-1"	1'-3"
2x8	13'-1"	11'-10"	9'-8"	1'-10"	2'-0"	2'-4"
2x10	16'-2"	14'-0"	11'-5"	3'-1"	3'-5"	2'-10"
2x12	18'-0"	16'-6"	13'-6"	4'-6"	4'-2"	3'-4"

Design this deck in 3D, free

Carries over: species, spacing, and a deck depth of 13 ft, which gives a joist span of about 10 ft. Not carried: deck width, height, and the joist size, which the designer works out for the whole deck. This table sizes joists only, not the beam, posts or footings.

Planning figures from the AWC DCA 6-2015 guide, not an engineer's design or a permit. Your building department has the final word, and local rules may be stricter.

Joist span table

Allowable joist span and overhang by size and spacing, DCA 6 Table 2. Spans are measured between supports, and overhang may not pass a quarter of the span. Joist length is limited to 18'-0".

Southern Pine
Joist	Span 12 in	Span 16 in	Span 24 in	Overhang 12 in	Overhang 16 in	Overhang 24 in
2x6	9'-11"	9'-0"	7'-7"	1'-0"	1'-1"	1'-3"
2x8	13'-1"	11'-10"	9'-8"	1'-10"	2'-0"	2'-4"
2x10	16'-2"	14'-0"	11'-5"	3'-1"	3'-5"	2'-10"
2x12	18'-0"	16'-6"	13'-6"	4'-6"	4'-2"	3'-4"

Douglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir
Joist	Span 12 in	Span 16 in	Span 24 in	Overhang 12 in	Overhang 16 in	Overhang 24 in
2x6	9'-6"	8'-4"	6'-10"	0'-11"	1'-0"	1'-2"
2x8	12'-6"	11'-1"	9'-1"	1'-8"	1'-10"	2'-2"
2x10	15'-8"	13'-7"	11'-1"	2'-10"	3'-2"	2'-9"
2x12	18'-0"	15'-9"	12'-10"	4'-4"	3'-11"	3'-3"

The northern group is Douglas Fir-Larch, Hem-Fir and Spruce-Pine-Fir. The table carries one row for the three, and it follows Hem-Fir, so each of them meets it.

Beam span table

Allowable beam span between posts, DCA 6 Table 3A, by the length of joists the beam carries. A beam may run past the end post by up to a quarter of its span, and no beam in the table spans more than 18'-0".

Southern Pine
Beam	Joists 6 ft	Joists 8 ft	Joists 10 ft	Joists 12 ft	Joists 14 ft	Joists 16 ft	Joists 18 ft
2-ply 2x6	6'-8"	5'-8"	5'-1"	4'-7"	4'-3"	4'-0"	3'-9"
2-ply 2x8	8'-6"	7'-4"	6'-6"	5'-11"	5'-6"	5'-1"	4'-9"
3-ply 2x6	7'-11"	7'-2"	6'-5"	5'-10"	5'-5"	5'-0"	4'-9"
2-ply 2x10	10'-1"	8'-9"	7'-9"	7'-1"	6'-6"	6'-1"	5'-9"
3-ply 2x8	10'-7"	9'-3"	8'-3"	7'-6"	6'-11"	6'-5"	6'-1"
2-ply 2x12	11'-11"	10'-4"	9'-2"	8'-4"	7'-9"	7'-3"	6'-9"
3-ply 2x10	12'-9"	11'-0"	9'-9"	8'-9"	8'-3"	7'-8"	7'-3"
3-ply 2x12	15'-0"	13'-0"	11'-7"	10'-6"	9'-9"	9'-1"	8'-7"

Douglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir
Beam	Joists 6 ft	Joists 8 ft	Joists 10 ft	Joists 12 ft	Joists 14 ft	Joists 16 ft	Joists 18 ft
2-ply 2x6	5'-2"	4'-5"	3'-11"	3'-7"	3'-3"	2'-10"	2'-6"
2-ply 2x8	6'-7"	5'-8"	5'-1"	4'-7"	4'-3"	3'-10"	3'-5"
3-ply 2x6	7'-1"	6'-5"	5'-9"	5'-3"	4'-10"	4'-6"	4'-3"
2-ply 2x10	8'-1"	7'-0"	6'-3"	5'-8"	5'-3"	4'-10"	4'-5"
3-ply 2x8	9'-5"	8'-3"	7'-4"	6'-8"	6'-2"	5'-9"	5'-5"
2-ply 2x12	9'-5"	8'-2"	7'-3"	6'-7"	6'-1"	5'-8"	5'-4"
3-ply 2x10	11'-9"	10'-2"	9'-1"	8'-3"	7'-7"	7'-1"	6'-8"
3-ply 2x12	13'-8"	11'-10"	10'-6"	9'-7"	8'-10"	8'-3"	7'-10"

Try your own numbers in the deck beam span calculator.

Post height and footing table

Maximum height of a 6x6 post, from grade or the top of the footing up to the underside of the beam, and the footing under it, DCA 6 Table 4. Heights are in feet. NP means not permitted. An 8x8 post may replace a 6x6 anywhere in the table, up to 14 ft. Footings assume soil that bears 1,500 psf and 2,500 psi concrete.

Maximum 6x6 post height in feet, by species, and footing size in inches
Beam span up to	Joists up to	Southern Pine	Douglas Fir-Larch	Hem-Fir, Western Cedars	Redwood	Ponderosa Pine, Red Pine, SPF	Footing round / square / thick
6 ft	10 ft	14 ft	14 ft	14 ft	14 ft	14 ft	18 / 16 / 7
6 ft	14 ft	14 ft	14 ft	14 ft	14 ft	14 ft	21 / 18 / 8
6 ft	18 ft	14 ft	14 ft	12 ft	14 ft	11 ft	24 / 21 / 10
8 ft	10 ft	14 ft	14 ft	14 ft	14 ft	14 ft	20 / 18 / 8
8 ft	14 ft	14 ft	14 ft	14 ft	14 ft	11 ft	24 / 21 / 10
8 ft	18 ft	14 ft	13 ft	11 ft	12 ft	8 ft	27 / 24 / 11
10 ft	10 ft	14 ft	14 ft	14 ft	14 ft	12 ft	23 / 20 / 9
10 ft	14 ft	14 ft	13 ft	11 ft	13 ft	8 ft	27 / 24 / 11
10 ft	18 ft	12 ft	11 ft	8 ft	11 ft	2 ft	31 / 27 / 13
12 ft	10 ft	14 ft	14 ft	12 ft	14 ft	10 ft	25 / 22 / 10
12 ft	14 ft	13 ft	12 ft	9 ft	11 ft	5 ft	30 / 26 / 13
12 ft	18 ft	11 ft	9 ft	6 ft	9 ft	2 ft	34 / 30 / 15
14 ft	10 ft	14 ft	13 ft	11 ft	13 ft	8 ft	27 / 24 / 11
14 ft	14 ft	11 ft	10 ft	7 ft	10 ft	2 ft	32 / 29 / 14
14 ft	18 ft	9 ft	8 ft	2 ft	8 ft	NP	37 / 33 / 16
16 ft	10 ft	13 ft	12 ft	10 ft	12 ft	6 ft	29 / 26 / 12
16 ft	14 ft	10 ft	9 ft	5 ft	9 ft	2 ft	35 / 31 / 15
16 ft	18 ft	7 ft	5 ft	2 ft	7 ft	NP	40 / 35 / 18
18 ft	10 ft	12 ft	11 ft	8 ft	11 ft	2 ft	31 / 27 / 13
18 ft	14 ft	9 ft	8 ft	2 ft	8 ft	NP	37 / 33 / 16
18 ft	18 ft	5 ft	2 ft	2 ft	6 ft	NP	42 / 37 / 19

Size footings for a whole deck in the deck footing calculator.

How to use the tables

Start with the joists: find the size that spans your distance at your spacing. Then take the longest joist length and read the beam table to see how far apart the posts can be. Last, take the beam span and the joist length to the post table for the height and footing. The calculators at the top of each page do these steps for you and highlight the cell they used.

Where the numbers come from

Every limit on this page is read from the American Wood Council, Prescriptive Residential Wood Deck Construction Guide (DCA 6), 2015 edition, a guide written for the 2015 International Residential Code. The deck designer, the builder's plan and these tools all read the same tables. The span tables assume 40 psf live load, 10 psf dead load, No. 2 grade lumber in wet service, and footings on soil that bears at least 1,500 psf.

A number that is our own choice and not in the guide, such as the 24 in joist overhang we draw by default, is never presented as a code requirement. Where a value comes from somewhere other than DCA 6, the page says so.

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Questions

Anything else? Write to us or see every calculator.

Questions people ask

Not as a deck joist. DCA 6 limits deck joist spans to 18'-0", and the best a 2x12 does in Table 2 is 18'-0", in Southern Pine at 12 in on center. For 20 ft, add a beam to split the span.

Table 2 is written for 12, 16, 24 in on center, and closer joists span further. Your decking sets the real limit: 1 in thick wood boards go on joists up to 16 in apart, 2 in thick wood on joists up to 24 in, and composite follows the maker's instructions, commonly 16 in.

They apply to decks inside the limits of DCA 6: 40 psf live load, no hot tubs, snow load up to 40 psf, attached decks no deeper than they are wide, and soil that bears 1,500 psf. A deck outside those limits needs an engineer. Your local building department may also have its own tables.