Deck Joist Span Table — IRC 2021 Table R507.6

What this chart answers

Almost every deck framing question resolves to one of two lookups: how far can this joist span, and how far can this beam span. The joist half lives in Table R507.6 of the IRC, and it is the table people search for by size — "deck joist span chart 2×8", "how far can a 2×10 span" — because the answer changes with four variables at once and nobody wants to reason it out from first principles on a job site.

This page reproduces R507.6 in full. Every cell matches the published table, including the maximum-cantilever columns that most reproductions drop, and the conditions the numbers are valid under are printed below rather than buried in a PDF footnote.

What the chart assumes — the conditions that travel with the numbers

A span table is a set of answers to one specific question. R507.6 rates No. 2 grade lumber at wet-service, with a 10 psf dead load already included, a main span held to L/360 and a cantilever held to L/180 with a 220 lb point load applied to its end. The table has four column groups by load: 40 psf live and 50, 60 and 70 psf ground snow. Snow is not assumed to act at the same time as the live load, so you size for whichever is higher, never both.

The reason a 2×10 will hold far more than these numbers before it actually breaks is that almost every span here is set by deflection, not strength. A joist that is strong enough but springy feels wrong underfoot and works against the ledger connection, so the code caps how far a member may flex. L/360 means a 14 ft joist may sag no more than 14 × 12 ÷ 360 = 0.47″.

The deck joist span chart — Table R507.6, cell for cell

All four load cases are below. Read across a row for the maximum span at 12″, 16″ and 24″ on centre, then continue into the maximum-cantilever columns, which are keyed on the joist back span. "NP" is the code's shorthand for not permitted.

The size-by-size answer — Southern pine, 40 psf live

Most decks are the 40 psf live-load case, and most decks in the southern pine belt are built with Southern pine, so the four rows below answer the great majority of "how far can a ___ span" searches. The numbers are straight out of the first block of the chart above.

• 2×6 — 9-11 at 12″ OC, 9-0 at 16″, 7-7 at 24″. The shortest span in the table; a 2×6 deck joist is really only for a small, low, closely-spaced deck.
• 2×8 — 13-1 at 12″ OC, 11-10 at 16″, 9-8 at 24″. The workhorse for a raised deck framed at 12″ on centre.
• 2×10 — 16-2 at 12″ OC, 14-0 at 16″, 11-5 at 24″. The default choice for a deck around 12 to 14 ft deep framed at 16″ on centre.
• 2×12 — 18-0 at 12″ OC, 16-6 at 16″, 13-6 at 24″. 18-0 is the largest value that appears anywhere in Table R507.6.

Species moves the numbers, and it moves them most at the longer spans. At 16″ on centre with a 2×10, Southern pine gives 14-0, the Douglas fir-larch / hem-fir / spruce-pine-fir group gives 13-7, and the redwood, western cedar, ponderosa pine and red pine group gives 13-0. Half a foot is easy to lose on a mixed load of lumber, which is why the species group is a column and not a footnote.

Load case moves them more. The same Southern pine 2×10 at 16″ on centre goes 14-0 under 40 psf live, 13-9 at 50 psf snow, 12-9 at 60 psf and 11-11 at 70 psf. If your jurisdiction lists a ground snow load on the permit, you are in one of the last three columns and a design that worked on paper for a 14 ft span no longer fits.

How far can a 2×10 span? — joist, beam and header

"How far can a 2×10 span" is the most common size-specific framing question on the site, and it has no single answer, because a 2×10 is not one thing. The same nominal board spans 16-2 (16 ft 2 in) as a deck joist at 12″ on centre but only about 9 ft as a doubled deck beam — and lands on a different figure again as a header, a floor joist or a rafter, each from its own table on its own load and deflection basis. The two deck cases are side by side below, because they are what the question almost always means.

As a deck joist

The joist answer is a straight read of Table R507.6, and it is the one most people want. For Southern pine No. 2 at 40 psf live load a 2×10 spans 16-2 at 12″ on centre, 14-0 at 16″ and 11-5 at 24″. Species and load move it: switch to the Douglas fir-larch / hem-fir / spruce-pine-fir group and 16″ on centre drops to 13-7; switch the load to a 70 psf ground snow case and the same Southern pine 2×10 at 16″ falls to 11-11. Two feet of span turns on species and another two on load, so "how far can a 2×10 span" is a range, never a number.

As a deck beam

The beam answer is not a straight read, because the beam tables are entered with an effective joist span — the actual joist span multiplied by the Table R507.5(5) factor. For a plain deck with no joist cantilever that factor is 0.66, so a 12 ft actual joist span reads the beam table at 12 × 0.66 = 7.92 ft, the 8 ft effective-span column. In that column a Southern pine 2×10 arranged as a doubled beam spans 9-0 between posts; tripled, it spans 11-2. Change the effective span to 10 ft and the doubled 2×10 drops to 8-0.

Worked example: a doubled 2×10 under 12 ft joists

A Southern pine deck, 40 psf live, joists running 12 ft from the ledger to the beam with no cantilever, and posts spaced 10 ft along the beam. How far can the 2×10 beam reach?

• Effective joist span. 12 ft × 0.66 = 7.92 ft, so read the 8 ft column of Table R507.5(1).
• Single 2×10. 6-0 — it cannot bridge a 10 ft post spacing. A single-ply beam is not a 2×10 you would actually build.
• Doubled 2×10. 9-0. That is still short of the 10 ft post spacing, so the two-ply beam fails too.
• Tripled 2×10. 11-2, which clears 10 ft. This is the answer — three plies of 2×10, or the same beam with the posts pulled in to 9 ft.

The arithmetic is one multiplication and one table read, and it is the same hand-off the section below spells out in full: joists first, then the R507.5(5) factor, then the beam.

The member decides — a 2×10 is not a 2×10

The reason a single span figure cannot answer the question is that each member has its own table and its own basis. A floor joist is sized from R502.3 and Tables R502.3.1(1) and (2), which split sleeping areas (30 psf live) from other rooms (40 psf) and use a different deflection limit from a deck. A header over a door or window comes from Table R602.7(1) and depends on the building width and ground snow, not on joist spacing. A rafter is a roof member sized to the roof load and span. Crossing a size from one of those tables into another is a framing error, not a shortcut.

The practical version: a 2×10 that looks comfortable as a deck joist at 14 ft is not a 14 ft header, and the floor-joist table will not hand you a deck number. Size each member from its own table — the header size calculator runs R602.7, the deck beam span chart carries R507.5(1), and this page carries R507.6 — and if a member falls outside its table, that is a designer's job, not a bigger number.

The cantilever column, and why it is separate

A deck joist that overhangs its beam carries extra load at the support, so the IRC does not fold the cantilever into the main span. Table R507.6 gives a maximum cantilever for each back span from 4 ft to 18 ft, and where no cantilever is allowed at that back span the cell reads NP. For Southern pine 2×10 at 40 psf live, the allowed cantilever is 2-6 at a 10 ft back span, 3-0 at 12 ft, 3-4 at 14 ft or 16 ft, and NP at 18 ft.

The mechanism behind the column is the footnote: a cantilever is held to L/180 with a 220 lb point load at its end. That point load is a person standing on the edge or leaning on a railing, and it is what stops a long cantilever on a short back span. A cantilever also changes the beam that supports the joists, which is the next lookup.

Where the joist table hands off to the beam table

The beam tables (R507.5(1) through (4)) are entered not with the actual joist span but with an effective deck joist span: the actual span multiplied by a factor from Table R507.5(5) that depends on the ratio of joist cantilever to joist span.

This is the step that quietly decides beam size, and it only ever shortens the effective span, which reads a shorter column and permits a longer beam. The deck beam & joist span calculator walks both lookups together so you do not have to carry the factor across by hand, and the deck beam span chart carries the R507.5(1) beam table itself, cell for cell.

Worked example — a 12 ft span, checked by hand

A Southern pine deck, 40 psf live load, joists running 12 ft from the ledger face to the beam centre, framed at 16″ on centre. Which joist?

• Try the 2×8 at 16″. The 2×8 row of the 40 psf block gives 11-10 at 16″ on centre. 11-10 is 11.83 ft, which is short of your 12 ft. So the 2×8 fails at 16″.
• Step up to the 2×10 at 16″. 14-0 = 14.00 ft, which clears 12 ft with 2 ft of margin. This is the answer, and it is what a deck at this depth is normally framed with.
• Could you keep the 2×8? Only by tightening the spacing. The 2×8 at 12″ on centre reaches 13-1 = 13.08 ft and fits — at the cost of 12″ centres, more hangers and more lumber. This is the trade the table lets you make explicitly.
• What if you wanted 24″ centres? The 2×10 at 24″ is only 11-5, so it fails at 12 ft too, and you would need the 2×12 at 13-6. And whatever the joists do, 24″ spacing is only legal if the decking is rated for it (R507.7).

Every one of those four steps is a single cell of the chart above, and that is the point of a reference table over a calculator: you can see the alternatives in one glance instead of re-entering numbers.

Common mistakes with the deck joist chart

• Reading the 40 psf block when you have a snow load. If your jurisdiction lists a ground snow load, the 50, 60 or 70 psf block is the one that applies, and spans fall by up to two feet.
• Treating "NP" as a soft no. NP is the code declining to permit a cantilever at that back span. It is not a value to interpolate toward.
• Using the actual joist span for the beam lookup. The beam tables are entered with the effective span from Table R507.5(5), which for a plain deck is the actual span × 0.66. Reading the actual span is conservative but not what the code says.
• Mixing floor and deck tables. R502.3 and R507.6 use different live-load and deflection bases; a size that works in a floor table is not automatically good on a deck.
• Forgetting the decking limit. At 24″ on centre, a 1¼″ deck board will not span the gap in a multiple-span pattern — only 2″ decking does (Table R507.7). The deck board spacing guide walks the R507.7 spacing rules and the gap between boards.
• Assuming the top grade buys you a size. The table is No. 2 grade with the wet-service factor. Substituting a better species or grade is an engineering decision, not a table swap.

Deck joist span FAQ

Where these numbers came from

Table R507.6 and Table R507.5(5) were fetched on 2026-09-30 from the up.codes viewers for the 2021 IRC in two independent jurisdictions — the 2021 IRC portion of the 2022 Connecticut State Building Code (chapter 5, Floors) and the 2021 Virginia Residential Code — parsed cell by cell and diffed. Both viewers agree cell-for-cell on every row on this page, and a third viewer (Oregon 2021 ORSC) was used as a tiebreak. The footnotes quoted above (10 psf dead load, No. 2 grade wet-service, L/360 main span, L/180 with a 220 lb point load at the cantilever, interpolation permitted) are read verbatim from the same page. The IRC is adopted state by state: check your own edition and amendments, and the authority having jurisdiction always wins.

This is a working reference, not engineering. A table lookup is the right answer only while your situation sits inside the table — inside the span, inside the load, inside the conditions above. Anything outside it, or any deck carrying unusual loads, needs a designer or an engineer.

Related pages

• Deck beam & joist span calculator — the same tables applied to one layout, including the R507.5(5) factor
• Deck footing size calculator — the posts and pads that carry whatever the joists land on
• Deck post spacing guide — sizing and spacing the posts the beam rests on, and the footing under each one
• Deck stairs guide — step count, stringer spacing and the landing rule
• Deck board spacing — the decking and its gaps, which set the maximum joist spacing
• Reference tables — every code table, with its source and verification date
• Roof pitch chart — pitch to degrees, slope multiplier and rafter length, for the roof above the deck framing