SpanRef

Lumber span reference

How far can that joist, rafter, or beam span?

Look up allowable spans straight from the published code tables - floor joists, ceiling joists, rafters, and decks - for every species, grade, size, and spacing. Instant lookup, a deck calculator, and a “what size do I need” reverse tool. Every value cites its source.

Look up a spanBrowse the span tables
2x1015′-5″16″ o.c.

SPF #2 floor joist, 40 psf live load

1,002
Published span values
4
Species: SPF, DF-L, SYP, Hem-Fir
IRC + AWC
Code-recognized source tables
100%
Free reference & tools

Every framing member

Span tables by member type

Each table is reproduced verbatim from its published source, cited on the page.

Floor joist

Floor joistsHorizontal members that carry a floor's live and dead load between supports.

Rafter

RaftersSloped roof members that carry roof and snow loads down to the walls.

Ceiling joist

Ceiling joistsHorizontal members that carry a ceiling and any limited attic storage.

Decks

Deck joists & beamsDCA6 deck joist spans, overhangs, and beam sizes for residential decks.

Popular lookups

Common span questions

Floor joist2x8 · Douglas Fir-Larch16″ o.c.12′-9″#2 gradeFloor joist2x10 · Spruce-Pine-Fir16″ o.c.15′-5″#2 gradeFloor joist2x12 · Southern Pine16″ o.c.16′-6″#2 gradeFloor joist2x8 · Spruce-Pine-Fir16″ o.c.13′-6″#2 gradeRafter2x10 · Douglas Fir-Larch24″ o.c.15′-3″#2 gradeRafter2x8 · Spruce-Pine-Fir16″ o.c.15′-1″#2 grade

Guides

Learn to read the tables

Free guides that explain what the grids are actually saying - every figure they quote is taken from the tables on this site and linked back to the page it lives on.

How far can a 2x8 joist span?There is no single answer. See the published 2x8 spans by species, grade, spacing and load case, and what the span table leaves out.6 min readJoist spacing: 16 in vs 24 in on centerWhat on-center spacing means, what a 2x8 or 2x10 actually loses going from 16 in to 24 in, and when the wider layout is worth it.6 min readWhat does L/360 deflection mean?L/360 is a deflection limit: the span divided by 360. Here is the arithmetic, why floors, ceilings and rafters use different limits, and what it changes.6 min read
All guides

Plan a whole build

Size every member, then get a takeoff

The project planner lets you add each floor, roof, or deck member, check it against its published span, and pull the material takeoff - all free. Premium prints the finished packet as an inspector sheet and exports it as CSV or JSON. It runs entirely in your browser - no account, no sign-up.

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