Lumber span reference

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

SpanRef is a free lumber span reference for builders and DIYers: allowable spans for floor joists, ceiling joists, rafters, and decks, from the 2018 IRC span tables and the AWC DCA6 deck guide, for every species, grade, size, and spacing, with the source cited for every value.

Look up a span Browse the span tables

SPF #2 floor joist, 40 psf live load

1,002

Published span values

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 grade Floor joist2x10 · Spruce-Pine-Fir16″ o.c.15′-5″#2 grade Floor joist2x12 · Southern Pine16″ o.c.16′-6″#2 grade Floor joist2x8 · Spruce-Pine-Fir16″ o.c.13′-6″#2 grade Rafter2x10 · Douglas Fir-Larch24″ o.c.15′-3″#2 grade Rafter2x8 · 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 read Joist 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 read What 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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