Ceiling joist span calculator: how far can a ceiling joist span?

17 ft 8 in

Table R802.5.1(1) · 19 ft 6 in at 12 in · 16 ft 8 in at 19.2 in · 15 ft 0 in at 24 in · 13 ft 0 in with limited storage · for Douglas fir-larch #2, no attic storage

Run your own numbers

A 2 × 6 Douglas fir-larch No. 2 ceiling joist at 16 inches on center spans up to 17 ft 8 in under an attic without storage (IRC 2021 Table R802.5.1(1)), and 13 ft 0 in under an attic with limited storage.

A worked example

A 2 × 10 Spruce-pine-fir No. 2 ceiling joist at 19.2 in on center under an attic with limited storage needs a room no wider than 18 ft 2 in between bearing walls. That is the Table R802.5.1(2) cell for 19.2 in spacing, Spruce-pine-fir No. 2 and 2 × 10. Checked against a room 17 ft 9 in wide it clears by 5 in; a 2 × 8 stops at 17 ft 1 in even in select structural, so at this spacing that room takes a 2 × 10 No. 2 or better. With no attic storage the same 2 × 10 spans 25 ft 8 in.

How far can a 2x6 ceiling joist span without support?

With nothing under it between the bearing walls, a 2 × 6 Douglas fir-larch No. 2 at 16 inches on center spans 17 ft 8 in under an attic without storage and 13 ft 0 in with limited storage; at 24 inches, 15 ft 0 in and 10 ft 8 in. At 16 inches with no storage, the 2 × 6 runs from 12 ft 11 in in Southern pine No. 3 to 18 ft 9 in in Douglas fir-larch select structural.

How far can a 2x8 ceiling joist span?

At 16 inches on center under an attic without storage: 23 ft 4 in in Douglas fir-larch No. 2, 22 ft 4 in in Spruce-pine-fir No. 2, 21 ft 9 in in Hem-fir No. 2 and 21 ft 7 in in Southern pine No. 2. Limited storage cuts the Douglas fir-larch to 16 ft 6 in. A 2 × 10 No. 2 at 16 inches passes 26 ft, where the table stops, in every species but Southern pine, 25 ft 7 in.

How far can a 2x4 ceiling joist span?

A 2 × 4 Douglas fir-larch No. 2 spans 11 ft 3 in at 16 inches on center with no attic storage and 8 ft 11 in with limited storage; at 24 inches, 9 ft 10 in and 7 ft 3 in. The 2 × 4 column starts at 13 ft 2 in, Douglas fir-larch select structural at 12 inches, and ends at 5 ft 1 in, Southern pine No. 3 at 24 inches with storage.

What else it is called

Also searched as a ceiling joist span chart or table, with storage or without, or as “how far can a 2x6 ceiling joist span without support”. The span is the distance between the walls the joists bear on; Section R802.5 has them run continuous across the house or join over an interior wall. Footnote g of Table R301.5 puts the 20 psf of limited storage only where the attic opening is at least 20 by 30 in, the joists slope 2 in 12 or less and the insulation is shallower than the joists; the rest of the ceiling carries 10 psf.

The IRC ceiling joist span tables

IRC 2021 Table R802.5.1(1), uninhabitable attics without storage (10 psf live load, 5 psf dead load), and Table R802.5.1(2), uninhabitable attics with limited storage (20 psf live load, 10 psf dead load), both at L/Δ = 240, as printed: feet-inches (17-8 is 17 ft 8 in). Note a: Span exceeds 26 feet in length. Check sources for availability of lumber in lengths greater than 20 feet.

Where the numbers come from

• Spans: 2021 International Residential Code, Section R802.5.1 and Tables R802.5.1(1), Ceiling Joist Spans for Common Lumber Species under uninhabitable attics without storage (10 psf live load, 5 psf dead load), and R802.5.1(2), the same under attics with limited storage (20 psf live load, 10 psf dead load), printed in full below. Both hold deflection to L/240, and note a marks every span over 26 ft. Read October 31, 2026, in the code text published by UpCodes, after a cell by cell match with the model text in the 2021 Seattle Residential Code. Read the code
• Which table: IRC 2021 Table R301.5, notes b and g. An attic with 42 in or less of clear height between joists and rafters is without storage; with 42 in or more, or two or more adjacent trusses with room for a 42 by 24 in rectangle, it has limited storage. Read October 31, 2026. Table R301.5
• Nothing here is calculated: the page reads the cell for your attic, spacing, species, grade and size, and for a span you type it lists every size and grade at your spacing whose cell reaches it.

By Javier Miralles · Last updated October 31, 2026. How this site is made.

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