Structural span › Beams
Beam Span Calculator and Wood Beam Span Chart
Pick plies, size and building width and get the maximum span for a built-up 2x beam straight from IRC 2021 Table R602.7. Free, no signup, printable.
The longest span in the IRC beam table is 15 ft 7 in. — four plies of 2×12, on a 12 ft wide house, under one floor only. On a typical 24–36 ft wide house the same beam tops out at 11 ft 0 in. to 9 ft 0 in.
This table covers 2× dimension-lumber beams and headers only. Building a deck beam? Use the deck beam span calculator — it uses a different IRC table. Sizing a door or window opening? See the header size calculator. Looking at LVL, glulam or steel? Jump to where this table stops.
How to use the beam span calculator
You don't need to know load, deflection or modulus of elasticity to use this — the table already has them built in. You only need four things you can measure or find on your plans:
- What the beam carries — roof and ceiling only, an interior floor, or an open porch. This picks the table (R602.7(1), (2) or (3)).
- Building width — measured perpendicular to the ridge, in feet. Round up to the next bucket (12, 24 or 36 ft) if you're between sizes.
- Ground snow load — 30, 50 or 70 psf, for exterior walls and porches only. Use your local building department's number, or 30 psf if the ground snow load is under 30 psf and roof live load is 20 psf or less.
- Beam size you want to check — e.g. double 2×10, triple 2×12 — or leave it blank to see every size that reaches your span.
The result shows the maximum span, the number of plies, and the jack studs required at each end (not shown for porch beams — the IRC table doesn't specify them there).
Wood beam span chart from IRC Table R602.7
Three tables cover every built-up 2× beam: interior girders under a floor, beams in exterior bearing walls, and open-porch beams. All values are No.2 grade — Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir give the same span (see why species doesn't change the number).
Load-bearing beam span table: interior beams under one or two floors
IRC 2021 Table R602.7(2). Use this for a girder inside the house — a wall you're thinking about removing, a basement beam, or a flush beam under a second-floor wall.
| Beam size | 12 ft wide | 24 ft wide | 36 ft wide |
|---|---|---|---|
| 2-2x8 | 7′ 9″ | 5′ 5″ | 4′ 5″ |
| 2-2x10 | 9′ 2″ | 6′ 6″ | 5′ 3″ |
| 2-2x12 | 10′ 9″ | 7′ 7″ | 6′ 3″ |
| 3-2x8 | 9′ 8″ | 6′ 10″ | 5′ 7″ |
| 3-2x10 | 11′ 5″ | 8′ 1″ | 6′ 7″ |
| 3-2x12 | 13′ 6″ | 9′ 6″ | 7′ 9″ |
| 4-2x8 | 11′ 2″ | 7′ 11″ | 6′ 5″ |
| 4-2x10 | 13′ 3″ | 9′ 4″ | 7′ 8″ |
| 4-2x12 | 15′ 7″ | 11′ 0″ | 9′ 0″ |
| Beam size | 12 ft wide | 24 ft wide | 36 ft wide |
|---|---|---|---|
| 2-2x8 | 5′ 0″ | 3′ 8″ | 3′ 1″ |
| 2-2x10 | 5′ 11″ | 4′ 4″ | 3′ 7″ |
| 2-2x12 | 6′ 11″ | 5′ 2″ | 4′ 3″ |
| 3-2x8 | 6′ 3″ | 4′ 7″ | 3′ 10″ |
| 3-2x10 | 7′ 5″ | 5′ 6″ | 4′ 6″ |
| 3-2x12 | 8′ 8″ | 6′ 5″ | 5′ 4″ |
| 4-2x8 | 7′ 2″ | 5′ 4″ | 4′ 5″ |
| 4-2x10 | 8′ 6″ | 6′ 4″ | 5′ 3″ |
| 4-2x12 | 10′ 1″ | 7′ 5″ | 6′ 2″ |
Building width = the width of roof and floor the wall above actually carries, perpendicular to the ridge — see how to measure it. Jack studs (1–3 per end) are in the calculator, not repeated here.
Beam span table for exterior bearing walls
IRC 2021 Table R602.7(1), 30 psf ground snow load (use this if your ground snow load is under 30 psf and roof live load is 20 psf or less). At 50 or 70 psf snow, spans run 5–20% shorter — the calculator above covers all three; see a worked comparison in beam span and size questions.
| Beam size | 12 ft wide | 24 ft wide | 36 ft wide |
|---|---|---|---|
| 2-2x8 | 7′ 7″ | 5′ 9″ | 4′ 10″ |
| 2-2x10 | 9′ 0″ | 6′ 10″ | 5′ 9″ |
| 2-2x12 | 10′ 7″ | 8′ 1″ | 6′ 10″ |
| 3-2x8 | 9′ 5″ | 7′ 3″ | 6′ 1″ |
| 3-2x10 | 11′ 3″ | 8′ 7″ | 7′ 3″ |
| 3-2x12 | 13′ 2″ | 10′ 1″ | 8′ 6″ |
| 4-2x8 | 10′ 11″ | 8′ 4″ | 7′ 0″ |
| 4-2x10 | 12′ 11″ | 9′ 11″ | 8′ 4″ |
| 4-2x12 | 15′ 3″ | 11′ 8″ | 9′ 10″ |
Porch beam span chart
IRC 2021 Table R602.7(3), open porch supporting a roof, 30 psf snow. Porch depth is measured from the house wall to the centerline of the beam. This table has no jack-stud column and assumes wet-service, incised lumber.
| Beam size | 8 ft deep porch | 14 ft deep porch |
|---|---|---|
| 2-2x6 | 7′ 6″ | 5′ 8″ |
| 2-2x8 | 10′ 1″ | 7′ 7″ |
| 2-2x10 | 12′ 4″ | 9′ 4″ |
| 2-2x12 | 14′ 4″ | 10′ 10″ |
Double 2×8 beam span
A double 2×8 spans 4 ft 5 in. to 7 ft 9 in. as an interior girder (12–36 ft wide house, one floor), or 4 ft 10 in. to 7 ft 7 in. in an exterior wall. Two floors above roughly halves it — 3 ft 1 in. to 5 ft 0 in.
Double 2×10 beam span
A double 2×10 spans 5 ft 3 in. to 9 ft 2 in. interior (one floor) or 5 ft 9 in. to 9 ft 0 in. exterior, depending on building width. On a porch (30 psf, 8 ft deep) it reaches 12 ft 4 in.
Double 2×12 beam span
A double 2×12 spans 6 ft 3 in. to 10 ft 9 in. interior (one floor), 6 ft 10 in. to 10 ft 7 in. exterior. It is the largest 2-ply size in the table — go to triple or quadruple plies for more, or to LVL.
Triple 2×10 beam span
A triple 2×10 spans 6 ft 7 in. to 11 ft 5 in. interior (one floor), 7 ft 3 in. to 11 ft 3 in. exterior — roughly 25% more than a double 2×10, not 50%, because deflection (not just bending) governs the longer spans.
Triple 2×12 beam span
A triple 2×12 spans 7 ft 9 in. to 13 ft 6 in. interior (one floor), 8 ft 6 in. to 13 ft 2 in. exterior. This is the size in the "triple 2x12 for a 20 ft span" question below — and the table stops well short of 20 ft even at three plies.
What the beam span table shows that rules of thumb miss
Across every species, ply count, width and condition in Table R602.7, just ten combinations clear a 12 ft span — and every one of them is either a 12 ft wide building or an 8 ft deep porch. On a normal 24–36 ft wide house, even a four-ply 2×12 caps out around 9–11 ft. "Just add another 2x12" runs out of table long before it runs out of forum advice.
Across all 51 comparable width/condition cells in the table, a 3-ply 2×8 beats a 2-ply 2×10 on span. Depth matters more than raw lumber count assumes, and section modulus (which drives the comparison) scales with the square of depth — three 8-inch plies simply out-stiffen two 10-inch ones.
In every one of the 51 matching cells, 4-2×10 comes in under 3-2×12 — even though a 4-2x10 uses more total lumber. Depth beats ply count again. If you're choosing between the two for a given span, the triple 2×12 is the shallower, stronger, and usually cheaper option.
A four-ply 2×12 girder spans 15 ft 7 in. supporting one floor, but only 10 ft 1 in. supporting two — a 35% cut from doubling the load. Anyone sizing a beam for a two-story addition off a one-story span number is undersizing it.
Table R602.7 gives one combined span for Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir at No.2 grade — all four are identical in every cell. Species selection matters for floor joists and rafters (different tables), but not for a No.2 built-up beam sized from this table.
Several sizing guides list a double 2×12 as good for an 8–10 ft opening under one story. Table R602.7(1) actually gives 8 ft 1 in. at a 24 ft wide building and 6 ft 10 in. at 36 ft — a rule of thumb that ignores building width overstates the span by a foot or more on a typical house.
How to measure beam span, house width and what the beam carries
Beam span vs. beam length
Span is the clear distance between supports — walls, posts or footings — not the physical length of the lumber. A 12 ft beam resting on a post 4 ft from one end has an 8 ft clear span on the long side, not 12 ft. Every number on this page is a clear span; measure between the centers of your supports, not the ends of the boards.
Building width, and why it changes the beam span
Building width is measured perpendicular to the ridge, and it isn't a cosmetic input — it's a stand-in for how much roof, floor and wall load funnels down onto your beam. A wider building means a wider tributary area feeding that wall, so the same beam has to carry more load and its allowable span drops. That's why a double 2×10 spans 9 ft 2 in. on a 12 ft wide building but only 5 ft 3 in. on a 36 ft wide one — same beam, roughly triple the load. If your width falls between the table's 12/24/36 ft columns, the code permits interpolation (note c); this calculator rounds up to the next column instead, which is always the conservative choice. For the load itself, see the beam load / tributary area calculator.
Center-bearing vs. clear-span floor (interior table only)
Table R602.7(2) splits "one floor" and "two floors," and each floor can be center-bearing (the floor joists themselves are supported partway across, by another beam or wall) or clear-span (the joists run the full width with no mid-support). A center-bearing floor puts less load on your girder than a clear-span floor of the same width — this table uses the more conservative clear-span assumption throughout, so it's safe by default.
Ground snow load
For exterior-wall and porch beams, pick 30, 50 or 70 psf ground snow load from your local building department. If your actual ground snow load is under 30 psf and your roof live load is 20 psf or less, the code lets you use the 30 psf column (note e) — that covers most of the southern and coastal US.
Built-up beam rules: nailing, bearing and notching
Plies have to match
The table assumes equal-depth plies nailed together as one member — a triple 2×12 is three matching 2×12s, not a 2×8 with 2×12s sistered on. Adding lumber to an existing beam to stretch its span only works if every ply runs the full new span and matches the others in depth; a mismatched sandwich doesn't map onto this table at all.
Does plywood between the plies make it stronger?
No — a plywood spacer between two 2x plies is a width filler, not a strength contributor. It's there so a doubled 2× beam matches a standard 3½ in. wall thickness (two 1½ in. plies plus a ½ in. spacer). The beam's span capacity comes entirely from the lumber plies; the plywood does not add to the section the table is sized on.
Nailing a built-up beam (IRC Table R602.3(1), item 28)
Built-up girders and beams made of 2-inch lumber layers are nailed with 20d common (or 10d box, or equivalent) nails at 32 in. on center at the top and bottom, staggered on opposite sides — plus 2 nails at every end and at every splice. This is a code minimum for holding the plies together as one member, separate from the span table itself.
Bearing at each end (R502.6)
Each end of the beam needs at least 1½ in. of bearing on wood or metal, or 3 in. on masonry or concrete — with a minimum 48 sq in. bearing area under a sill plate if it's bearing on masonry directly. Undersized bearing causes crushing at the support, a separate failure mode from an undersized span.
Joists framing into the side of a beam (R502.6.2)
Where floor joists frame into the side of the beam rather than sitting on top of it, they need approved joist hangers or a 2x2 ledger strip — a joist simply nailed to the side isn't a code connection.
Notching and drilling (R502.8.1, R502.8.2)
Solid-sawn beams follow the same notch limits as joists: notches capped at 1/6 of the depth, none in the middle third of the span, end notches capped at 1/4 depth. Engineered beams (LVL, glulam, I-joists) can't be notched or drilled at all except where the manufacturer's literature specifically allows it — there is no prescriptive IRC allowance for cutting into them.
Unbraced top — the 0.70 factor
If the top of a 2×8, 2×10 or 2×12 header or girder isn't laterally braced by framing above it (for example, cripple studs bearing on it rather than full-height studs beside it), the code requires multiplying the tabulated span by 0.70, or having the member individually designed. This note appears on the exterior-wall table R602.7(1) and the interior table R602.7(2); the porch table R602.7(3) carries no equivalent note.
Positive connection at posts (R502.9)
Where a beam sits on posts rather than a continuous wall, the code requires a positive connection against uplift and lateral displacement — not just gravity bearing. A beam resting loose on a post cap doesn't meet this on its own; it needs a mechanical tie.
When a wood beam will not span: 4x/6x timbers, LVL, glulam and steel
Table R602.7 covers 2× dimension lumber plies only — up to four plies of 2×12, topping out at 15 ft 7 in. under the single best-case condition. Past that, or for anything the table doesn't cover, here's what's actually available and why this calculator doesn't size it:
- Solid 4x6, 6x6, 6x8, 6x12 timbers aren't in Table R602.7 at all — the prescriptive path only covers built-up 2x plies. A solid timber beam needs an engineered size or a manufacturer/reference span table of its own.
- LVL (laminated veneer lumber) is sized from the manufacturer's own proprietary span tables (Weyerhaeuser, Boise Cascade, LP and others), not the IRC. Those tables aren't independently verifiable the way IRC tables are, so this site doesn't reproduce LVL numbers — see beam span and size questions: 4x6, LVL, 20-ft spans for how to read a manufacturer's LVL table.
- Glulam and PSL beams follow the same pattern — manufacturer-specific design values, sized with the maker's software or span tool, not a code table.
- Steel beams (W-shapes) and flitch beams are a structural design exercise, not a prescriptive lookup, in every case.
Manufacturers publish their own free sizing tools for their products, and most lumberyards that sell LVL or glulam can run a size for you from your span and load. For a full structural check on any beam — deflection, bending stress, shear, not just a table lookup — see beam deflection and moment of inertia explained and live load vs. dead load.
What's below the beam matters too
Sizing the beam is only half the load path. Every post under it needs its own adequate footing, and where a continuous basement or foundation beam is replaced by point loads at posts, the load concentrates at those points instead of spreading out — see the deck post size calculator and deck footing size calculator for the deck-side version of that check. Most jurisdictions require a permit and inspection for any beam that carries structural load, and anything outside a standard table condition — unusual loads, long spans, multiple stories, an existing beam you're not sure about — is worth a licensed engineer's sign-off before you cut into anything.
Deck beam, floor beam, header or ridge beam: which span table
"Beam" gets used for several different framing members. Match yours to the right table before you read a span off any chart:
| Your beam | IRC table | Tool |
|---|---|---|
| Interior wall you might remove, basement beam | IRC R602.7(2) | This page — interior table above |
| Wall in an exterior bearing wall | IRC R602.7(1) | This page — exterior table above |
| Open porch beam | IRC R602.7(3) | This page — porch table above |
| Deck beam (outdoors, deck load) | IRC R507.5(1)–(4) | Deck beam span calculator |
| Door or window header, jack studs | IRC R602.7(1) | Header size calculator |
| Floor joist (not a beam) | IRC R502.3.1 | Floor joist span calculator |
| Roof rafter (not a beam) | IRC R802.4.1(1)–(8) | Rafter span calculator |
| Ridge beam or roof beam | No prescriptive IRC table | See where this table stops — engineered per project |
Beam size examples: 12 ft, 16 ft and 20 ft spans
A kitchen wall comes out; the second floor above is supported center-bearing on that wall, house is 24 ft wide. From the interior table (one floor, 24 ft wide): a double 2×12 only reaches 7 ft 7 in., a triple 2×12 reaches 9 ft 6 in., and a four-ply 2×12 reaches 11 ft 0 in. — still short of 12 ft. At 24 ft wide, no 2x built-up beam in this table clears a 12 ft span; this is exactly where an LVL or engineered beam takes over.
A contractor installs a double 2×12 (with a plywood spacer, not adding strength) across a 16 ft opening. The table's longest double-2x12 span is 10 ft 9 in. (12 ft wide, one floor, best case) — nowhere near 16 ft under any condition in Table R602.7(2). A double 2×12 does not cover a 16 ft span at any building width; this size is table-appropriate only for spans under about 11 ft.
Even the table's absolute maximum — four plies of 2×12 on a 12 ft wide building under one floor — only reaches 15 ft 7 in., and a triple 2×12 tops out at 13 ft 6 in. under the same best-case condition. A 20 ft span is off this table entirely at any ply count; it needs LVL, glulam, a steel beam, or an intermediate post to break the span into two shorter ones the table can size.
Frequently asked questions
How far can a triple 2x12 beam span?
A triple 2x12 spans 7 ft 9 in. to 13 ft 6 in. under IRC Table R602.7, depending on whether it's interior or exterior, one or two floors, and building width — see the full breakdown by ply count and condition in beam span and size questions: 4x6, LVL, 20-ft spans.
What size beam do I need for a 12 foot span?
It depends on building width and what floors above it carries. On a 24 ft wide house with one floor above, a four-ply 2x12 girder reaches 11 ft 0 in. — still short of 12 ft, so 12 ft at that width is off this table and needs LVL or an engineered beam. On a 12 ft wide building, a triple 2x12 already clears 12 ft (13 ft 6 in.). Enter your own width and floor count in the calculator above rather than using a single rule of thumb.
What size beam do I need for a 20 foot span?
Nothing in Table R602.7 reaches 20 ft — the table's absolute maximum, at any width, ply count or condition, is 15 ft 7 in. A 20 ft opening needs LVL, glulam, a steel beam, or an intermediate post splitting it into two shorter table-sized spans.
Can a double 2x12 beam span 16 feet?
No. The longest span any double 2x12 reaches in Table R602.7 is 10 ft 9 in. (12 ft wide house, one floor, interior). A double 2x12 does not cover a 16 ft span under any building width or loading condition — a beam installed at that size on a 16 ft opening would need engineering review or replacement with a larger built-up beam or LVL.
What size beam do I need to remove a load-bearing wall?
It depends on the span, the building width, and how many floors the wall carries — there's no single answer. Enter your span and width into the calculator above to check whether a 2x built-up beam covers it; if the span is over roughly 11–15 ft (depending on width) even a four-ply 2x12 won't reach it and you'll need LVL, glulam or steel. Any load-bearing wall removal should also be reviewed by whoever pulls your permit.
How far can a double 2x10 beam span without support?
A double 2x10 spans 5 ft 3 in. to 9 ft 2 in. as an interior girder (one floor, 36–12 ft wide) or 5 ft 9 in. to 9 ft 0 in. in an exterior wall, per IRC Table R602.7. "Without support" here means between its two end bearings — adding a mid-span post changes the span to the shorter distance on each side, not the full beam length.
Why does beam span depend on the width of the house?
Building width stands in for how much roof, floor and wall load funnels down onto that wall's beam — a wider building means more tributary area and more load, so the same beam spans less. It's not the beam's own length that changes; it's how much weight is riding on it. See how building width is measured above.
Is beam span the length of the beam or the distance between posts?
It's the clear distance between supports — walls, posts or footings — not the physical length of lumber you buy. A 12 ft beam with a post 4 ft in from one end has an 8 ft clear span on that side and a 4 ft clear span on the other, not a single 12 ft span.
Does plywood between 2x12s make a beam stronger?
No. A plywood spacer between two lumber plies fills width to match a standard 3½ in. wall (two 1½ in. plies plus a ½ in. spacer) — it doesn't add to the beam's load-carrying section. The table's span comes entirely from the lumber plies themselves.
Can I add 2x12s to an existing 2x8 beam to extend its span?
Only if the added plies run the full new span and match the original in depth — a beam built from mismatched depths (say, one 2x8 sistered with 2x12s) doesn't correspond to any single row in Table R602.7. In practice, extending an existing beam's span usually means replacing it outright with a properly sized built-up beam or LVL rather than adding mismatched plies.
My beam hasn't sagged in years — does that mean it meets code?
Not necessarily. A beam can perform acceptably under its actual, lighter-than-designed-for loading for years and still be undersized for the loads the code assumes (snow, full occupancy live load, a future renovation). Absence of visible sag isn't a substitute for checking the size against the table, especially before adding any new load above it.
How far can a 4x6 or 6x6 beam span?
Solid-sawn 4x and 6x timbers aren't covered by IRC Table R602.7 at all — that table only sizes built-up 2x plies. A solid timber beam needs its own span reference or an engineered size; see beam span and size questions for how those are typically sized.
Does wood species change the beam span?
No, not in this table. IRC Table R602.7 gives one combined span for Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir at No.2 grade — all four are identical in every cell. Species selection does matter for floor joists and rafters, which use different tables.
Can I use this chart for an LVL, a ridge beam, or a post-and-beam frame?
No. LVL is sized from manufacturer-specific span tables, not the IRC. A ridge beam and heavy-timber post-and-beam framing have no prescriptive IRC table at all and are sized by engineering or manufacturer data. This page covers 2x built-up dimension-lumber beams and headers only — see where this table stops.
What is the difference between a beam, a girder and a header?
Structurally they're the same kind of member — a horizontal piece carrying load down to its supports — and IRC Table R602.7 sizes all of them with the same tables. "Header" usually means one over a door or window opening; "girder" or "beam" usually means a longer structural member inside or under the house, such as one replacing a load-bearing wall.
Source and verification of these beam spans
Every span comes from IRC 2021 Tables R602.7(1), R602.7(2) and R602.7(3), as printed in the 2021 Seattle Residential Code, Chapter 6, pages 6-15 to 6-18 — a verbatim IRC reproduction with no local amendment affecting these three tables. R502.5 (Chapter 5, page 5-8) is what makes this the correct girder table: "the allowable spans of girders and headers fabricated of dimension lumber shall not exceed the values set forth in Tables R602.7(1), R602.7(2) and R602.7(3)." An 18-cell sample was checked against the printed tables with zero mismatches; full methodology: how these calculators are checked.
This calculator applies the 0.70 unbraced-top factor to header/girder spans exactly as printed on Tables R602.7(1) and R602.7(2); that note does not appear on the porch table R602.7(3), and porch results here do not apply it. These tables cover No.2-grade dimension lumber beams only — for LVL, glulam, steel or solid timber, see where this table stops.