Reference · 2021 IRC (official) and 2018 IRC

Deck span tables

The prescriptive tables behind every Deckwright calculator, laid out for reading on a phone or printing for the job site. The 2021 tables are transcribed from the official ICC text and checked by hash against it. Use the edition your building department has adopted, and check its amendments.

Joist span calculator Beam calculator

These tables show the 40 psf live load case. The 2021 IRC also has 50, 60 and 70 psf ground-snow tables, which our calculators use when you select a snow load. All values assume No. 2 grade lumber, wet service and a 10 psf dead load. Where a table allows interpolation, our calculators read the more restrictive neighboring column instead. NP = not permitted.

2021 IRC Table R507.6: deck joist spans and cantilevers

Maximum span from the ledger or beam to the supporting beam, and the maximum cantilever past the beam by the joist’s back span. A cantilever may also not exceed ¼ of the actual back span.

Southern pine
Size	Span @ 12″	Span @ 16″	Span @ 24″	Cant. @ 4′ back span	Cant. @ 6′ back span	Cant. @ 8′ back span	Cant. @ 10′ back span	Cant. @ 12′ back span	Cant. @ 14′ back span	Cant. @ 16′ back span	Cant. @ 18′ back span
2x6	9′-11″	9′-0″	7′-7″	1′-0″	1′-6″	1′-5″	NP	NP	NP	NP	NP
2x8	13′-1″	11′-10″	9′-8″	1′-0″	1′-6″	2′-0″	2′-6″	2′-3″	NP	NP	NP
2x10	16′-2″	14′-0″	11′-5″	1′-0″	1′-6″	2′-0″	2′-6″	3′-0″	3′-4″	3′-4″	NP
2x12	18′-0″	16′-6″	13′-6″	1′-0″	1′-6″	2′-0″	2′-6″	3′-0″	3′-6″	4′-0″	4′-1″

Douglas fir-larch, hem-fir, spruce-pine-fir
Size	Span @ 12″	Span @ 16″	Span @ 24″	Cant. @ 4′ back span	Cant. @ 6′ back span	Cant. @ 8′ back span	Cant. @ 10′ back span	Cant. @ 12′ back span	Cant. @ 14′ back span	Cant. @ 16′ back span	Cant. @ 18′ back span
2x6	9′-6″	8′-4″	6′-10″	1′-0″	1′-6″	1′-4″	NP	NP	NP	NP	NP
2x8	12′-6″	11′-1″	9′-1″	1′-0″	1′-6″	2′-0″	2′-3″	2′-0″	NP	NP	NP
2x10	15′-8″	13′-7″	11′-1″	1′-0″	1′-6″	2′-0″	2′-6″	3′-0″	3′-3″	NP	NP
2x12	18′-0″	15′-9″	12′-10″	1′-0″	1′-6″	2′-0″	2′-6″	3′-0″	3′-6″	3′-11″	3′-11″

Redwood, western cedars, ponderosa pine, red pine
Size	Span @ 12″	Span @ 16″	Span @ 24″	Cant. @ 4′ back span	Cant. @ 6′ back span	Cant. @ 8′ back span	Cant. @ 10′ back span	Cant. @ 12′ back span	Cant. @ 14′ back span	Cant. @ 16′ back span	Cant. @ 18′ back span
2x6	8′-10″	8′-0″	6′-10″	1′-0″	1′-4″	1′-1″	NP	NP	NP	NP	NP
2x8	11′-8″	10′-7″	8′-8″	1′-0″	1′-6″	2′-0″	1′-11″	NP	NP	NP	NP
2x10	14′-11″	13′-0″	10′-7″	1′-0″	1′-6″	2′-0″	2′-6″	3′-0″	2′-9″	NP	NP
2x12	17′-5″	15′-1″	12′-4″	1′-0″	1′-6″	2′-0″	2′-6″	3′-0″	3′-6″	3′-8″	NP

2021 IRC Table R507.5(1): deck beam spans

Maximum distance between posts, by the effective joist span: the actual joist span × a factor from Table R507.5(5) (0.66 with no cantilever, 0.72 at C/J = 1/12, 0.80 at 1/10, 0.84 at 1/8, 0.90 at 1/6, 1.00 at 1/4). A beam may overhang its end post by up to ¼ of the beam span.

Southern pine
Beam	≤ 6 ft	≤ 8 ft	≤ 10 ft	≤ 12 ft	≤ 14 ft	≤ 16 ft	≤ 18 ft
(2) 2x6	6′-11″	5′-11″	5′-4″	4′-10″	4′-6″	4′-3″	4′-0″
(2) 2x8	8′-9″	7′-7″	6′-9″	6′-2″	5′-9″	5′-4″	5′-0″
(2) 2x10	10′-4″	9′-0″	8′-0″	7′-4″	6′-9″	6′-4″	6′-0″
(2) 2x12	12′-2″	10′-7″	9′-5″	8′-7″	8′-0″	7′-5″	7′-0″
(3) 2x6	8′-6″	7′-5″	6′-8″	6′-1″	5′-8″	5′-3″	4′-11″
(3) 2x8	10′-11″	9′-6″	8′-6″	7′-9″	7′-2″	6′-8″	6′-4″
(3) 2x10	13′-0″	11′-2″	10′-0″	9′-2″	8′-6″	7′-11″	7′-6″
(3) 2x12	15′-3″	13′-3″	11′-10″	10′-9″	10′-0″	9′-4″	8′-10″

Douglas fir-larch, hem-fir, spruce-pine-fir
Beam	≤ 6 ft	≤ 8 ft	≤ 10 ft	≤ 12 ft	≤ 14 ft	≤ 16 ft	≤ 18 ft
(2) 2x6	6′-1″	5′-3″	4′-9″	4′-4″	3′-11″	3′-7″	3′-3″
(2) 2x8	8′-2″	7′-1″	6′-4″	5′-9″	5′-2″	4′-8″	4′-4″
(2) 2x10	10′-0″	8′-7″	7′-9″	7′-0″	6′-6″	6′-0″	5′-6″
(2) 2x12	11′-7″	10′-0″	8′-11″	8′-2″	7′-7″	7′-1″	6′-8″
(3) 2x6	7′-8″	6′-8″	6′-0″	5′-6″	5′-1″	4′-9″	4′-6″
(3) 2x8	10′-3″	8′-10″	7′-11″	7′-3″	6′-8″	6′-3″	5′-11″
(3) 2x10	12′-6″	10′-10″	9′-8″	8′-10″	8′-2″	7′-8″	7′-2″
(3) 2x12	14′-6″	12′-7″	11′-3″	10′-3″	9′-6″	8′-11″	8′-5″

Redwood, western cedars, ponderosa pine, red pine
Beam	≤ 6 ft	≤ 8 ft	≤ 10 ft	≤ 12 ft	≤ 14 ft	≤ 16 ft	≤ 18 ft
(2) 2x6	6′-2″	5′-4″	4′-10″	4′-5″	4′-0″	3′-8″	3′-4″
(2) 2x8	7′-10″	6′-10″	6′-1″	5′-7″	5′-2″	4′-10″	4′-5″
(2) 2x10	9′-7″	8′-4″	7′-5″	6′-9″	6′-3″	5′-10″	5′-6″
(2) 2x12	11′-1″	9′-8″	8′-7″	7′-10″	7′-3″	6′-10″	6′-5″
(3) 2x6	7′-8″	6′-9″	6′-0″	5′-6″	5′-1″	4′-9″	4′-6″
(3) 2x8	9′-10″	8′-6″	7′-7″	6′-11″	6′-5″	6′-0″	5′-8″
(3) 2x10	12′-0″	10′-5″	9′-4″	8′-6″	7′-10″	7′-4″	6′-11″
(3) 2x12	13′-11″	12′-1″	10′-9″	9′-10″	9′-1″	8′-6″	8′-1″

2021 IRC Table R507.4: deck post heights

Maximum post height (top of footing to underside of beam) by the deck area each post carries. The IRC requires 6x6 minimum where the beam is notched into the post.

Southern pine
Post	≤ 20 sq ft	≤ 40 sq ft	≤ 60 sq ft	≤ 80 sq ft	≤ 100 sq ft	≤ 120 sq ft	≤ 140 sq ft	≤ 160 sq ft
4x4	14′-0″	13′-8″	11′-0″	9′-5″	8′-4″	7′-5″	6′-9″	6′-2″
4x6	14′-0″	14′-0″	13′-11″	12′-0″	10′-8″	9′-8″	8′-10″	8′-2″
6x6	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″
8x8	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″

Douglas fir-larch, hem-fir, spruce-pine-fir
Post	≤ 20 sq ft	≤ 40 sq ft	≤ 60 sq ft	≤ 80 sq ft	≤ 100 sq ft	≤ 120 sq ft	≤ 140 sq ft	≤ 160 sq ft
4x4	14′-0″	13′-6″	10′-10″	9′-3″	8′-0″	7′-0″	6′-2″	5′-3″
4x6	14′-0″	14′-0″	13′-10″	11′-10″	10′-6″	9′-5″	8′-7″	7′-10″
6x6	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″
8x8	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″

Redwood, western cedars, ponderosa pine, red pine
Post	≤ 20 sq ft	≤ 40 sq ft	≤ 60 sq ft	≤ 80 sq ft	≤ 100 sq ft	≤ 120 sq ft	≤ 140 sq ft	≤ 160 sq ft
4x4	14′-0″	13′-2″	10′-3″	8′-1″	5′-8″	NP	NP	NP
4x6	14′-0″	14′-0″	13′-6″	11′-4″	9′-9″	8′-4″	6′-9″	4′-7″
6x6	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	13′-7″	9′-7″
8x8	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″	14′-0″

2021 IRC Table R507.3.1: minimum footing size

By tributary area and soil bearing value (Table R401.4.1), 40 psf live load. Our calculators use the larger of this table and a load ÷ bearing calculation, with minimums of 12″ square and 14″ round.

Tributary area	1,500 psf soil			2,000 psf soil			≥ 3,000 psf soil
Tributary area	Square	Round Ø	Thick	Square	Round Ø	Thick	Square	Round Ø	Thick
5 sq ft	7″	8″	6″	7″	8″	6″	7″	8″	6″
20 sq ft	10″	12″	6″	9″	9″	6″	7″	8″	6″
40 sq ft	14″	16″	6″	12″	14″	6″	10″	12″	6″
60 sq ft	17″	19″	6″	15″	17″	6″	12″	14″	6″
80 sq ft	20″	22″	7″	17″	19″	6″	14″	16″	6″
100 sq ft	22″	25″	8″	19″	21″	6″	15″	17″	6″
120 sq ft	24″	27″	9″	21″	23″	7″	17″	19″	6″
140 sq ft	26″	29″	10″	22″	25″	8″	18″	21″	6″
160 sq ft	28″	31″	11″	24″	27″	9″	20″	22″	7″

Ledger fastener spacing (Table R507.9.1.3(1), 40 psf)

On-center spacing of ½″ fasteners connecting a 2x ledger to a 1½″ lumber band joist, with up to ½″ sheathing between. Stagger the fasteners in two rows. The 2021 table also lists 50–70 psf snow loads, which our planner uses.

Joist span	≤ 6′	6′-1″ – 8′	8′-1″ – 10′	10′-1″ – 12′	12′-1″ – 14′	14′-1″ – 16′	16′-1″ – 18′
½″ lag screw	30″	23″	18″	15″	13″	11″	10″
½″ through-bolt	36″	36″	34″	29″	24″	21″	19″

2018 IRC tables (for jurisdictions still on 2018)

From published reproductions of the 2018 IRC. The 2018 edition sizes joist cantilevers by spacing rather than back span, uses a flat post-height table, and has no snow-load tables. Our calculators use these values only when you select the 2018 edition.

Joists, 2018 Table R507.6: Southern pine
Size	Span @ 12″	Span @ 16″	Span @ 24″	Cant. @ 12″	Cant. @ 16″	Cant. @ 24″
2x6	9′-11″	9′-0″	7′-7″	1′-3″	1′-4″	1′-6″
2x8	13′-1″	11′-10″	9′-8″	2′-1″	2′-3″	2′-5″
2x10	16′-2″	14′-0″	11′-5″	3′-4″	3′-6″	2′-10″
2x12	18′-0″	16′-6″	13′-6″	4′-6″	4′-2″	3′-4″

Joists, 2018 Table R507.6: Douglas fir-larch, hem-fir, spruce-pine-fir
Size	Span @ 12″	Span @ 16″	Span @ 24″	Cant. @ 12″	Cant. @ 16″	Cant. @ 24″
2x6	9′-6″	8′-4″	6′-10″	1′-2″	1′-3″	1′-5″
2x8	12′-6″	11′-1″	9′-1″	1′-11″	2′-1″	2′-3″
2x10	15′-8″	13′-7″	11′-1″	3′-1″	3′-5″	2′-9″
2x12	18′-0″	15′-9″	12′-10″	4′-6″	3′-11″	3′-3″

Joists, 2018 Table R507.6: Redwood, western cedars, ponderosa pine, red pine
Size	Span @ 12″	Span @ 16″	Span @ 24″	Cant. @ 12″	Cant. @ 16″	Cant. @ 24″
2x6	8′-10″	8′-0″	6′-10″	1′-0″	1′-1″	1′-2″
2x8	11′-8″	10′-7″	8′-8″	1′-8″	1′-10″	2′-0″
2x10	14′-11″	13′-0″	10′-7″	2′-8″	2′-10″	2′-8″
2x12	17′-5″	15′-1″	12′-4″	3′-10″	3′-9″	3′-1″

Beams, 2018 Table R507.5: Southern pine
Beam	joist span ≤ 6 ft	joist span ≤ 8 ft	joist span ≤ 10 ft	joist span ≤ 12 ft	joist span ≤ 14 ft	joist span ≤ 16 ft	joist span ≤ 18 ft
(1) 2x6	4′-11″	4′-0″	3′-7″	3′-3″	3′-0″	2′-10″	2′-8″
(1) 2x8	5′-11″	5′-1″	4′-7″	4′-2″	3′-10″	3′-7″	3′-5″
(1) 2x10	7′-0″	6′-0″	5′-5″	4′-11″	4′-7″	4′-3″	4′-0″
(1) 2x12	8′-3″	7′-1″	6′-4″	5′-10″	5′-5″	5′-0″	4′-9″
(2) 2x6	6′-11″	5′-11″	5′-4″	4′-10″	4′-6″	4′-3″	4′-0″
(2) 2x8	8′-9″	7′-7″	6′-9″	6′-2″	5′-9″	5′-4″	5′-0″
(2) 2x10	10′-4″	9′-0″	8′-0″	7′-4″	6′-9″	6′-4″	6′-0″
(2) 2x12	12′-2″	10′-7″	9′-5″	8′-7″	8′-0″	7′-6″	7′-0″
(3) 2x6	8′-2″	7′-5″	6′-8″	6′-1″	5′-8″	5′-3″	5′-0″
(3) 2x8	10′-10″	9′-6″	8′-6″	7′-9″	7′-2″	6′-8″	6′-4″
(3) 2x10	13′-0″	11′-3″	10′-0″	9′-2″	8′-6″	7′-11″	7′-6″
(3) 2x12	15′-3″	13′-3″	11′-10″	10′-9″	10′-0″	9′-4″	8′-10″

Beams, 2018 Table R507.5: All other species groups
Beam	joist span ≤ 6 ft	joist span ≤ 8 ft	joist span ≤ 10 ft	joist span ≤ 12 ft	joist span ≤ 14 ft	joist span ≤ 16 ft	joist span ≤ 18 ft
(2) 2x6 or 3x6	5′-5″	4′-8″	4′-2″	3′-10″	3′-6″	3′-1″	2′-9″
(2) 2x8 or 3x8	6′-10″	5′-11″	5′-4″	4′-10″	4′-6″	4′-1″	3′-8″
(2) 2x10 or 3x10	8′-4″	7′-3″	6′-6″	5′-11″	5′-6″	5′-1″	4′-8″
(2) 2x12 or 3x12	9′-8″	8′-5″	7′-6″	6′-10″	6′-4″	5′-11″	5′-7″
4x6	6′-5″	5′-6″	4′-11″	4′-6″	4′-2″	3′-11″	3′-8″
4x8	8′-5″	7′-3″	6′-6″	5′-11″	5′-6″	5′-2″	4′-10″
4x10	9′-11″	8′-7″	7′-8″	7′-0″	6′-6″	6′-1″	5′-8″
4x12	11′-5″	9′-11″	8′-10″	8′-1″	7′-6″	7′-0″	6′-7″
(3) 2x6	7′-4″	6′-8″	6′-0″	5′-6″	5′-1″	4′-9″	4′-6″
(3) 2x8	9′-8″	8′-6″	7′-7″	6′-11″	6′-5″	6′-0″	5′-8″
(3) 2x10	12′-0″	10′-5″	9′-4″	8′-6″	7′-10″	7′-4″	6′-11″
(3) 2x12	13′-11″	12′-1″	10′-9″	9′-10″	9′-1″	8′-6″	8′-1″

2018 Table R507.4 post heights: 4x4 and 4x6 up to 8′-0″ (4x4 to 6′-9″ under a 3-ply beam), 6x6 and 8x8 up to 14′-0″.

Sources and verification

2021 values were transcribed from the official 2021 IRC on ICC Digital Codes (codes.iccsafe.org, Chapter 5, Section R507). Our automated tests compare a SHA-256 hash of the data with one computed from the live ICC page. Two cells on ICC’s page are malformed (“604” and “6-22” / “5-20” in the redwood-group (3) 2x8 rows at 50 and 60 psf). We use the next, more restrictive column for those. 2018 values come from published reproductions (UpCodes; City of Brainerd, MN; Delhi Charter Township, MI). Details are on the methodology page. Found an error? Tell us.