How far can a 2 × 8 deck joist span?

At 16 in on center, 2 × 8 No. 2 joists may span 11 ft 1 in in Douglas fir-larch, hem-fir or spruce-pine-fir, 11 ft 10 in in Southern pine and 10 ft 7 in in redwood, western cedars, ponderosa pine and red pine, from the 2021 IRC Table R507.6. At 12 in on center the Douglas fir group goes to 12 ft 6 in; at 24 in it drops to 9 ft 1 in. The span is measured between the supports, not the length of the board.

What size joists do I need for a 12 foot span?

It depends on the species and spacing. For Douglas fir-larch, hem-fir or spruce-pine-fir, a 12 ft span takes 2 × 8, 2 × 10, 2 × 12 at 12 in, 2 × 10, 2 × 12 at 16 in and 2 × 12 at 24 in. In Southern pine it is 2 × 10, 2 × 12 at 16 in. The calculator lists these for the span you enter. The smallest size that passes leaves no room: a deck that feels bouncy often has joists at the limit, so many builders go up a size.

Which joist spacing should I use: 12, 16 or 24 inches?

Closer spacing allows a longer span: a 2 × 8 of the Douglas fir group spans 12 ft 6 in at 12 in, 11 ft 1 in at 16 in and 9 ft 1 in at 24 in. The decking also sets a limit. 16 in on center is the usual choice for 5/4 and 2 × decking laid straight across the joists, 24 in is for decking rated for it (many composites are not), and diagonal decking commonly needs 12 in. Check your decking's installation guide as well as the table.

How far can a deck joist cantilever past the beam?

The 2021 IRC limits a joist cantilever to one-fourth of the adjacent joist span, so a 10 ft span allows 2 ft 6 in. A cantilever no longer than the joist's nominal depth is allowed anyway. The code table also lists a maximum cantilever for each size and spacing that can be smaller than a quarter of the span, which this page does not reproduce, so look it up in the printed table for your size before you cantilever. A joist cut for a 10 ft span with a 24 in overhang is 12 ft long.

Does the span include the cantilever?

No. The table span is the distance between the two supports, such as the house ledger and the beam, measured to the center of bearing. The overhang past the beam is a cantilever and has its own limit, one-fourth of the joist span. The calculator takes the span in the “Joist span” field and the overhang in the cantilever field, and cuts the joist span plus cantilever long.

What if my span is longer than the table allows?

Add a beam under the middle of the deck to cut the span, move the beam, use a bigger joist, or go to a closer spacing. For example, a 2 × 6 at 16 in in the Douglas fir group spans only 8 ft 4 in, so a 10 ft span fails by 1 ft 8 in; a 2 × 8 or larger works. Past a 2 × 12 at 12 in (18 ft for most species), the table has no answer and an engineer or an engineered joist is needed.

What load is the table for, and when does it not apply?

It is for a residential deck with a 40 psf live load and 10 psf dead load, No. 2 grade lumber in wet service, and the ground snow loads the table covers. It does not cover a hot tub, a heavy planter, a roof or a pergola load on the joists, lumber below No. 2, higher snow loads (the 2021 code adds tables for 50, 60 and 70 psf ground snow), or composite and engineered joists. Use an engineer for any of those. Your local code and inspector govern, and some places amend the table.

How many joists do I need for my deck?

Joists = deck width in inches ÷ spacing, rounded up, plus one for the end joist. A 16 ft (192 in) wide deck at 16 in is 12 + 1 = 13 joists, and at 12 in it is 17. Add a rim joist across the outer ends of the joists, and a ledger against the house if the deck is attached. The deck boards calculator uses the same count for fasteners.

Are the Southern pine values different from the other species?

Yes. Southern pine is stronger, so its joists span farther: a 2 × 10 at 16 in spans 14 ft against 13 ft 7 in for Douglas fir-larch, hem-fir and spruce-pine-fir. Pressure-treated yellow pine is Southern pine. For lumber of another species, use that species' group from the table; if the stamp names a different group, ask the supplier.

Deck Joist Span Calculator: How Far Can a Deck Joist Span?

A 2 × 8 deck joist of Douglas fir-larch, hem-fir or spruce-pine-fir, 16 in on center, may span 11 ft 1 in (2021 IRC Table R507.6: 40 psf live load plus 10 psf dead load, No. 2 grade, wet service). A 10 ft span is inside that, with 1 ft 1 in to spare. A 16 ft wide deck at 16 in needs 13 joists (the end joist included), plus a 16 ft rim board and a 16 ft ledger. Pick the species group, size and spacing, and the page also lists every size that carries your span, the most the joists may cantilever, and the boards to buy. This is a residential deck table, not an engineered design: your local code and inspector govern.

Figures based on the sources listed belowUpdated 2026-10-18How we calculate

Deck width (along the house)

Joist span (house to beam)

Lumber species groupThe table groups species by strength. Pressure-treated southern yellow pine is Southern pine. The table assumes No. 2 grade; check the grade stamp or tag on the lumber.

Joist sizeNominal size. The table lists 2 × 6 through 2 × 12.

Joist spacingAlso limited by the decking: 24 in is only for decking rated for it; diagonal decking commonly needs 12 in.

Cantilever past the beam (in)

How far the joists overhang the beam, if at all. The joist is cut span plus this. The limit is 1/4 of the joist span, so a 10 ft span allows 30 in.

Attached to the house?A ledger board the width of the deck is added to the list. Freestanding decks have a second beam instead, which this tool does not size.

11 ft 1 in

Your 10 ft span with 2 × 8 at 16 in: within the table (1 ft 1 in to spare)
Sizes that carry 10 ft at 12 in: 2 × 8, 2 × 10, 2 × 12
Sizes that carry 10 ft at 16 in: 2 × 8, 2 × 10, 2 × 12
Sizes that carry 10 ft at 24 in: 2 × 10, 2 × 12
Cantilever limit (1/4 of the 10 ft span, or the 2 × 8 depth if more): 2' 6", the table’s own cap for the size may be lower
Joists (16 in on center, with the end joist): 13 joists (each cut 10 ft), from 10 ft 2 × 8s
Rim joist along the outer edge: 1 board (each 16 ft)
Ledger against the house: 1 board (each 16 ft), needs flashing and bolts per DCA 6
2 × 8 in the frame (joists + rim + ledger): 162 ft, before waste: buy a few extra

Shopping list

Joist hangers (2 × 8, galvanized or ZMAX)
Structural wood screws (ledger and rim)
Joist tape
Hurricane / joist ties
Flashing for a ledger
Chalk line

Show diagram

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Maximum deck joist spans by species group, size and spacing

Allowable span between supports, No. 2 grade, 40 psf live load plus 10 psf dead load, wet service, from the 2021 IRC Table R507.6 (DCA 6 Table 2). The redwood group row for 2 × 6 at 24 in (6 ft 10 in) is the more cautious of two values found; compare it with the printed table.
Species group	Size	12 in on center	16 in on center	24 in on center
Southern pine	2 × 6	9 ft 11 in	9 ft	7 ft 7 in
Southern pine	2 × 8	13 ft 1 in	11 ft 10 in	9 ft 8 in
Southern pine	2 × 10	16 ft 2 in	14 ft	11 ft 5 in
Southern pine	2 × 12	18 ft	16 ft 6 in	13 ft 6 in
Douglas fir-larch / hem-fir / SPF	2 × 6	9 ft 6 in	8 ft 4 in	6 ft 10 in
Douglas fir-larch / hem-fir / SPF	2 × 8	12 ft 6 in	11 ft 1 in	9 ft 1 in
Douglas fir-larch / hem-fir / SPF	2 × 10	15 ft 8 in	13 ft 7 in	11 ft 1 in
Douglas fir-larch / hem-fir / SPF	2 × 12	18 ft	15 ft 9 in	12 ft 10 in
Redwood / western cedars / ponderosa & red pine	2 × 6	8 ft 10 in	8 ft	6 ft 10 in
Redwood / western cedars / ponderosa & red pine	2 × 8	11 ft 8 in	10 ft 7 in	8 ft 8 in
Redwood / western cedars / ponderosa & red pine	2 × 10	14 ft 11 in	13 ft	10 ft 7 in
Redwood / western cedars / ponderosa & red pine	2 × 12	17 ft 5 in	15 ft 1 in	12 ft 4 in

Smallest joist for a span, Douglas fir-larch, hem-fir or spruce-pine-fir

The smallest size whose table span reaches the distance between supports, worked by this calculator. "none" means a 2 × 12 is not enough at that spacing.
Span	12 in on center	16 in on center	24 in on center
6 ft	2 × 6	2 × 6	2 × 6
8 ft	2 × 6	2 × 6	2 × 8
10 ft	2 × 8	2 × 8	2 × 10
12 ft	2 × 8	2 × 10	2 × 12
14 ft	2 × 10	2 × 12	none
16 ft	2 × 12	none	none
18 ft	2 × 12	none	none

Smallest joist for a span, Southern pine

The same lookup for Southern pine, which is a little stronger than the other groups.
Span	12 in on center	16 in on center	24 in on center
6 ft	2 × 6	2 × 6	2 × 6
8 ft	2 × 6	2 × 6	2 × 8
10 ft	2 × 8	2 × 8	2 × 10
12 ft	2 × 8	2 × 10	2 × 12
14 ft	2 × 10	2 × 10	none
16 ft	2 × 10	2 × 12	none
18 ft	2 × 12	none	none

Smallest joist for a span, redwood, western cedars, ponderosa pine and red pine

The same lookup for the third species group.
Span	12 in on center	16 in on center	24 in on center
6 ft	2 × 6	2 × 6	2 × 6
8 ft	2 × 6	2 × 6	2 × 8
10 ft	2 × 8	2 × 8	2 × 10
12 ft	2 × 10	2 × 10	2 × 12
14 ft	2 × 10	2 × 12	none
16 ft	2 × 12	none	none
18 ft	none	none	none

Joists by deck width

Joists = deck width in inches ÷ spacing, rounded up, plus one for the end joist. Worked by this calculator; the rim joist and the ledger are extra.
Deck width	12 in on center	16 in on center	24 in on center
8 ft	9	7	5
10 ft	11	9	6
12 ft	13	10	7
14 ft	15	12	8
16 ft	17	13	9
20 ft	21	16	11
24 ft	25	19	13

Cantilever limit by joist span

One-fourth of the adjacent joist span, with a cantilever no longer than the joist’s nominal depth always allowed (2 × 6 is 6 in, 2 × 12 is 12 in). The table’s own maximum for a size and spacing may be lower, so this is an upper bound.
Joist span	Limit (1/4 of span)	With a 2 × 6	With a 2 × 12
6 ft	1 ft 6 in	1 ft 6 in	1 ft 6 in
8 ft	2 ft	2 ft	2 ft
10 ft	2 ft 6 in	2 ft 6 in	2 ft 6 in
12 ft	3 ft	3 ft	3 ft
14 ft	3 ft 6 in	3 ft 6 in	3 ft 6 in
16 ft	4 ft	4 ft	4 ft

Methodology & assumptions

Maximum span: the number comes straight from the table of allowable spans for deck joists in the 2021 International Residential Code, Table R507.6, which is the joist table of the American Wood Council's Prescriptive Residential Wood Deck Construction Guide (DCA 6). It lists No. 2 grade lumber in three species groups (Southern pine; Douglas fir-larch, hem-fir and spruce-pine-fir; redwood, western cedars, ponderosa pine and red pine), nominal sizes 2 × 6 to 2 × 12, at 12, 16 and 24 in on center. The spans are calculated for a 40 psf live load plus a 10 psf dead load, with deflection limited to L/360 and lumber in wet service conditions (the usual state of outdoor wood). The span is the distance between the supports (the ledger or a beam), measured to the center of bearing. The table's values are exact, so the result is shown in feet and inches, not rounded. Does my span work? The entered span is compared with the table value, and the page shows how much is spare or how far over it is. Reverse lookup: for each of the three spacings, every size whose table span reaches yours is listed, smallest first; none means the span is longer than a 2 × 12 can carry at that spacing, so add a beam or ask an engineer. Cantilever: joists past the beam may overhang by at most one-fourth of the adjacent joist span (section R507.6), and an overhang no longer than the joist's nominal depth is permitted regardless. This tool shows that limit and checks your overhang against it. The table also gives a maximum cantilever for each size and spacing, which can be lower than a quarter of the span; those figures are not reproduced here, because the copies found disagreed. Check the printed table for the size you use when you cantilever, and never cantilever a joist that carries a hot tub or other concentrated load without an engineer. The joist is cut span plus cantilever long. Joist count: ceil(deck width in inches ÷ spacing) + 1, the extra one being the end joist; this is the same count as the deck boards calculator. A rim joist (the board across the outer ends) and, for a deck attached to the house, a ledger of the same length are added. Each is bought in the first stock length (8, 10, 12, 14, 16, 18 or 20 ft) that is at least as long, and a deck wider than 20 ft splices its rim over a joist. The linear feet total is joists plus rim plus ledger, before waste. What the table does not cover: snow loads above 40 psf ground snow (the 2021 code has separate tables for 50, 60 and 70 psf), other grades, lumber that is not No. 2, composite or engineered joists, joists that carry a hot tub, heavy planters or a roof, spans beyond 18 ft, guards and stairs, and the footings, beams, ledger attachment and connectors. DCA 6 caps spans at 18 ft. Decking limits the spacing separately: 16 in on center suits 5/4 and 2 × decking laid across the joists, 24 in only decking rated for it, and diagonal decking commonly needs 12 in. Treat the result as a lookup in a prescriptive table for a typical residential deck, with the local code and your inspector as the final authority; some jurisdictions amend the table.

International Code Council, 2021 International Residential Code, Section R507.6 Deck joists and Table R507.6 Deck joist spans for common lumber species (maximum spans for 40 psf live load plus 10 psf dead load, with the one-fourth span limit for joist cantilevers)
American Wood Council, Prescriptive Residential Wood Deck Construction Guide (DCA 6, 2015 edition), Table 2: joist spans for Southern pine; Douglas fir-larch, hem-fir and spruce-pine-fir; and redwood, western cedars, ponderosa pine and red pine; calculated for 40 psf live load, 10 psf dead load, L/360 deflection, No. 2 grade, wet service
Deck Joist Span Chart, IRC R507.6 Maximum Spans by Species & Spacing (reuven.tools): a reproduction of the table used to cross-check the Douglas fir-larch group and the redwood group
Deck Joist Span Calculator & Chart, IRC R507.6 Spans (measurethebuild.com): a second reproduction used to cross-check the Southern pine and redwood rows
Your local building department: the adopted code edition, ground snow load, amendments and the permit and inspection rules. The 2021 table is not in force everywhere, and some places still use the 2018 or 2015 edition

How to find the maximum deck joist span

Measure the joist span. Measure from the house ledger to the beam (center of bearing to center of bearing). That distance, not the board length, is the span.
Pick the species group, size and spacing. Find the lumber species on the grade stamp or tag, the nominal joist size, and the spacing, 12, 16 or 24 in on center.
Read the table value. Look up the maximum span for that group, size and spacing in 2021 IRC Table R507.6 (DCA 6 Table 2). It assumes No. 2 grade, 40 psf live load, 10 psf dead load and wet service.
Compare, and go up a size if it fails. Your span must be at or below the table value. If it is not, use a bigger joist, closer spacing or a beam to shorten the span.
Check the cantilever and count the joists. A joist may overhang the beam by at most one-fourth of its span. Joists = deck width in inches ÷ spacing, rounded up, plus one; add a rim joist and the ledger.

Worked examples

Project	Result
16 ft wide deck, 10 ft span, 2 × 8 Douglas fir-larch group at 16 in, on a ledger	11 ft 1 in allowed, 10 ft span fits; 13 joists of 10 ft, one 16 ft rim, one 16 ft ledger
The same deck at 12 in on center	12 ft 6 in allowed, 17 joists
The same deck with 2 × 6 joists	8 ft 4 in allowed: a 10 ft span is 1 ft 8 in too long
20 ft wide deck, 12 ft span, Southern pine 2 × 10 at 16 in	14 ft allowed, 12 ft span fits; 16 joists, rim and ledger in 20 ft boards
14 ft wide deck, 12 ft span, redwood 2 × 12 at 24 in	12 ft 4 in allowed, 12 ft span fits; 8 joists
12 ft wide freestanding deck, 8 ft span, 2 × 8 at 16 in with a 24 in cantilever	11 ft 1 in allowed, joists cut 10 ft long, 10 joists, cantilever limit 2 ft

Frequently asked questions

How far can a 2 × 8 deck joist span?: At 16 in on center, 2 × 8 No. 2 joists may span 11 ft 1 in in Douglas fir-larch, hem-fir or spruce-pine-fir, 11 ft 10 in in Southern pine and 10 ft 7 in in redwood, western cedars, ponderosa pine and red pine, from the 2021 IRC Table R507.6. At 12 in on center the Douglas fir group goes to 12 ft 6 in; at 24 in it drops to 9 ft 1 in. The span is measured between the supports, not the length of the board.
What size joists do I need for a 12 foot span?: It depends on the species and spacing. For Douglas fir-larch, hem-fir or spruce-pine-fir, a 12 ft span takes 2 × 8, 2 × 10, 2 × 12 at 12 in, 2 × 10, 2 × 12 at 16 in and 2 × 12 at 24 in. In Southern pine it is 2 × 10, 2 × 12 at 16 in. The calculator lists these for the span you enter. The smallest size that passes leaves no room: a deck that feels bouncy often has joists at the limit, so many builders go up a size.
Which joist spacing should I use: 12, 16 or 24 inches?: Closer spacing allows a longer span: a 2 × 8 of the Douglas fir group spans 12 ft 6 in at 12 in, 11 ft 1 in at 16 in and 9 ft 1 in at 24 in. The decking also sets a limit. 16 in on center is the usual choice for 5/4 and 2 × decking laid straight across the joists, 24 in is for decking rated for it (many composites are not), and diagonal decking commonly needs 12 in. Check your decking's installation guide as well as the table.
How far can a deck joist cantilever past the beam?: The 2021 IRC limits a joist cantilever to one-fourth of the adjacent joist span, so a 10 ft span allows 2 ft 6 in. A cantilever no longer than the joist's nominal depth is allowed anyway. The code table also lists a maximum cantilever for each size and spacing that can be smaller than a quarter of the span, which this page does not reproduce, so look it up in the printed table for your size before you cantilever. A joist cut for a 10 ft span with a 24 in overhang is 12 ft long.
Does the span include the cantilever?: No. The table span is the distance between the two supports, such as the house ledger and the beam, measured to the center of bearing. The overhang past the beam is a cantilever and has its own limit, one-fourth of the joist span. The calculator takes the span in the “Joist span” field and the overhang in the cantilever field, and cuts the joist span plus cantilever long.
What if my span is longer than the table allows?: Add a beam under the middle of the deck to cut the span, move the beam, use a bigger joist, or go to a closer spacing. For example, a 2 × 6 at 16 in in the Douglas fir group spans only 8 ft 4 in, so a 10 ft span fails by 1 ft 8 in; a 2 × 8 or larger works. Past a 2 × 12 at 12 in (18 ft for most species), the table has no answer and an engineer or an engineered joist is needed.
What load is the table for, and when does it not apply?: It is for a residential deck with a 40 psf live load and 10 psf dead load, No. 2 grade lumber in wet service, and the ground snow loads the table covers. It does not cover a hot tub, a heavy planter, a roof or a pergola load on the joists, lumber below No. 2, higher snow loads (the 2021 code adds tables for 50, 60 and 70 psf ground snow), or composite and engineered joists. Use an engineer for any of those. Your local code and inspector govern, and some places amend the table.
How many joists do I need for my deck?: Joists = deck width in inches ÷ spacing, rounded up, plus one for the end joist. A 16 ft (192 in) wide deck at 16 in is 12 + 1 = 13 joists, and at 12 in it is 17. Add a rim joist across the outer ends of the joists, and a ledger against the house if the deck is attached. The deck boards calculator uses the same count for fasteners.
Are the Southern pine values different from the other species?: Yes. Southern pine is stronger, so its joists span farther: a 2 × 10 at 16 in spans 14 ft against 13 ft 7 in for Douglas fir-larch, hem-fir and spruce-pine-fir. Pressure-treated yellow pine is Southern pine. For lumber of another species, use that species' group from the table; if the stamp names a different group, ask the supplier.

Handy tools

Feet and Inches Calculator: Measured 10' 3 1/2"? It turns tape readings into the decimal feet the span field takes.
Board Foot Calculator: Price the joists, rim and ledger by the board foot.