Span chart and checker
Floor joist span chart & calculator
Built for checking the floor you already have: enter the joist you measured under the house and see how much of the code-style span it uses, how bouncy it should feel, and what a damp crawl space or a plumber's notch does to it.
For checking, not designing: an engineer or the building department decides.
Last updated
Short answer
How far can a floor joist span?
A floor joist's maximum span depends on its size, spacing, species and grade. Under the common residential assumption (40 psf live, 10 psf dead, L/360), a No. 2 2x10 at 16 inches on center spans about 14 ft 0 in to 15 ft 7 in depending on species. Check your existing joist below — for checking, not design.
Span chart
Floor joist span chart
Maximum clear spans in feet-inches for 40 psf live load (living areas), 10 psf dead load and the L/360 deflection limit. Bedrooms-only (30 psf) tables are below each species.
Southern Pine — The usual framing lumber in the Southeast, including North Carolina.
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 11-1 | 10-1 | 9-6 | 8-10 |
| 2x6 No. 1 | 10-8 | 9-8 | 9-2 | 8-6 |
| 2x6 No. 2 | 10-3 | 9-3 | 8-6 | 7-7 |
| 2x6 No. 3 | 8-1 | 7-0 | 6-5 | 5-9 |
| 2x8 Select Structural | 14-8 | 13-4 | 12-6 | 11-7 |
| 2x8 No. 1 | 14-1 | 12-10 | 12-1 | 11-2 |
| 2x8 No. 2 | 13-6 | 11-9 | 10-9 | 9-7 |
| 2x8 No. 3 | 10-3 | 8-10 | 8-1 | 7-3 |
| 2x10 Select Structural | 18-9 | 17-0 | 16-0 | 14-10 |
| 2x10 No. 1 | 18-0 | 16-0 | 14-8 | 13-1 |
| 2x10 No. 2 | 16-2 | 14-0 | 12-9 | 11-5 |
| 2x10 No. 3 | 12-5 | 10-9 | 9-10 | 8-9 |
| 2x12 Select Structural | 22-9 | 20-8 | 19-6 | 18-1 |
| 2x12 No. 1 | 21-11 | 19-0 | 17-4 | 15-6 |
| 2x12 No. 2 | 19-0 | 16-6 | 15-0 | 13-5 |
| 2x12 No. 3 | 14-9 | 12-9 | 11-8 | 10-5 |
Southern Pine, 30 psf live load (sleeping rooms)
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 12-3 | 11-1 | 10-5 | 9-8 |
| 2x6 No. 1 | 11-9 | 10-8 | 10-1 | 9-4 |
| 2x6 No. 2 | 11-3 | 10-3 | 9-6 | 8-6 |
| 2x6 No. 3 | 9-1 | 7-10 | 7-2 | 6-5 |
| 2x8 Select Structural | 16-2 | 14-8 | 13-9 | 12-10 |
| 2x8 No. 1 | 15-6 | 14-1 | 13-3 | 12-4 |
| 2x8 No. 2 | 14-10 | 13-2 | 12-0 | 10-9 |
| 2x8 No. 3 | 11-5 | 9-11 | 9-1 | 8-1 |
| 2x10 Select Structural | 20-7 | 18-9 | 17-7 | 16-4 |
| 2x10 No. 1 | 19-10 | 17-11 | 16-4 | 14-8 |
| 2x10 No. 2 | 18-1 | 15-8 | 14-3 | 12-9 |
| 2x10 No. 3 | 13-11 | 12-1 | 11-0 | 9-10 |
| 2x12 Select Structural | 25-1 | 22-9 | 21-5 | 19-11 |
| 2x12 No. 1 | 24-1 | 21-3 | 19-5 | 17-4 |
| 2x12 No. 2 | 21-3 | 18-5 | 16-10 | 15-0 |
| 2x12 No. 3 | 16-6 | 14-3 | 13-0 | 11-8 |
Douglas Fir-Larch — Common in the West and sold nationwide; the stiffest of the four.
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 11-4 | 10-3 | 9-8 | 9-0 |
| 2x6 No. 1 | 10-11 | 9-11 | 9-4 | 8-8 |
| 2x6 No. 2 | 10-8 | 9-8 | 9-2 | 8-2 |
| 2x6 No. 3 | 8-10 | 7-8 | 7-0 | 6-3 |
| 2x8 Select Structural | 14-11 | 13-7 | 12-9 | 11-10 |
| 2x8 No. 1 | 14-5 | 13-1 | 12-3 | 10-11 |
| 2x8 No. 2 | 14-1 | 12-9 | 11-7 | 10-5 |
| 2x8 No. 3 | 11-3 | 9-9 | 8-10 | 7-11 |
| 2x10 Select Structural | 19-1 | 17-4 | 16-3 | 15-1 |
| 2x10 No. 1 | 18-4 | 16-5 | 15-0 | 13-5 |
| 2x10 No. 2 | 18-0 | 15-7 | 14-2 | 12-8 |
| 2x10 No. 3 | 13-9 | 11-11 | 10-10 | 9-8 |
| 2x12 Select Structural | 23-2 | 21-1 | 19-10 | 18-5 |
| 2x12 No. 1 | 22-0 | 19-0 | 17-4 | 15-6 |
| 2x12 No. 2 | 20-10 | 18-1 | 16-6 | 14-9 |
| 2x12 No. 3 | 15-11 | 13-9 | 12-7 | 11-3 |
Douglas Fir-Larch, 30 psf live load (sleeping rooms)
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 12-5 | 11-4 | 10-8 | 9-11 |
| 2x6 No. 1 | 12-0 | 10-11 | 10-3 | 9-6 |
| 2x6 No. 2 | 11-9 | 10-8 | 10-1 | 9-2 |
| 2x6 No. 3 | 9-11 | 8-7 | 7-10 | 7-0 |
| 2x8 Select Structural | 16-5 | 14-11 | 14-1 | 13-0 |
| 2x8 No. 1 | 15-10 | 14-5 | 13-6 | 12-3 |
| 2x8 No. 2 | 15-6 | 14-1 | 13-0 | 11-7 |
| 2x8 No. 3 | 12-7 | 10-10 | 9-11 | 8-10 |
| 2x10 Select Structural | 21-0 | 19-1 | 17-11 | 16-8 |
| 2x10 No. 1 | 20-3 | 18-4 | 16-9 | 15-0 |
| 2x10 No. 2 | 19-10 | 17-5 | 15-11 | 14-2 |
| 2x10 No. 3 | 15-4 | 13-3 | 12-1 | 10-10 |
| 2x12 Select Structural | 25-6 | 23-2 | 21-10 | 20-3 |
| 2x12 No. 1 | 24-7 | 21-3 | 19-5 | 17-4 |
| 2x12 No. 2 | 23-4 | 20-2 | 18-5 | 16-6 |
| 2x12 No. 3 | 17-10 | 15-5 | 14-1 | 12-7 |
Hem-Fir — Western hemlock and true firs; common in the West.
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 10-8 | 9-8 | 9-2 | 8-6 |
| 2x6 No. 1 | 10-5 | 9-6 | 8-11 | 8-3 |
| 2x6 No. 2 | 10-0 | 9-1 | 8-6 | 7-11 |
| 2x6 No. 3 | 8-8 | 7-6 | 6-10 | 6-1 |
| 2x8 Select Structural | 14-1 | 12-10 | 12-1 | 11-2 |
| 2x8 No. 1 | 13-9 | 12-6 | 11-9 | 10-10 |
| 2x8 No. 2 | 13-2 | 11-11 | 11-3 | 10-1 |
| 2x8 No. 3 | 10-11 | 9-6 | 8-8 | 7-9 |
| 2x10 Select Structural | 18-0 | 16-4 | 15-5 | 14-3 |
| 2x10 No. 1 | 17-7 | 16-0 | 14-9 | 13-3 |
| 2x10 No. 2 | 16-9 | 15-1 | 13-10 | 12-4 |
| 2x10 No. 3 | 13-5 | 11-7 | 10-7 | 9-5 |
| 2x12 Select Structural | 21-11 | 19-11 | 18-9 | 17-4 |
| 2x12 No. 1 | 21-5 | 18-10 | 17-2 | 15-4 |
| 2x12 No. 2 | 20-3 | 17-7 | 16-0 | 14-4 |
| 2x12 No. 3 | 15-6 | 13-5 | 12-3 | 11-0 |
Hem-Fir, 30 psf live load (sleeping rooms)
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 11-9 | 10-8 | 10-1 | 9-4 |
| 2x6 No. 1 | 11-6 | 10-5 | 9-10 | 9-2 |
| 2x6 No. 2 | 11-0 | 10-0 | 9-4 | 8-8 |
| 2x6 No. 3 | 9-8 | 8-4 | 7-8 | 6-10 |
| 2x8 Select Structural | 15-6 | 14-1 | 13-3 | 12-4 |
| 2x8 No. 1 | 15-2 | 13-9 | 13-0 | 12-1 |
| 2x8 No. 2 | 14-6 | 13-2 | 12-4 | 11-4 |
| 2x8 No. 3 | 12-3 | 10-7 | 9-8 | 8-8 |
| 2x10 Select Structural | 19-10 | 18-0 | 16-11 | 15-9 |
| 2x10 No. 1 | 19-5 | 17-7 | 16-6 | 14-9 |
| 2x10 No. 2 | 18-6 | 16-9 | 15-5 | 13-10 |
| 2x10 No. 3 | 15-0 | 13-0 | 11-10 | 10-7 |
| 2x12 Select Structural | 24-1 | 21-11 | 20-7 | 19-1 |
| 2x12 No. 1 | 23-7 | 21-0 | 19-2 | 17-2 |
| 2x12 No. 2 | 22-6 | 19-7 | 17-11 | 16-0 |
| 2x12 No. 3 | 17-4 | 15-0 | 13-9 | 12-3 |
Spruce-Pine-Fir — Canadian lumber common in the North and Midwest. No.1 and No.2 share one grade (No.1/No.2).
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 10-5 | 9-6 | 8-11 | 8-3 |
| 2x6 No. 1 | 10-3 | 9-3 | 8-9 | 8-1 |
| 2x6 No. 2 | 10-3 | 9-3 | 8-9 | 8-1 |
| 2x6 No. 3 | 8-8 | 7-6 | 6-10 | 6-1 |
| 2x8 Select Structural | 13-9 | 12-6 | 11-9 | 10-11 |
| 2x8 No. 1 | 13-6 | 12-3 | 11-5 | 10-3 |
| 2x8 No. 2 | 13-6 | 12-3 | 11-5 | 10-3 |
| 2x8 No. 3 | 10-11 | 9-6 | 8-8 | 7-9 |
| 2x10 Select Structural | 17-7 | 16-0 | 15-1 | 14-0 |
| 2x10 No. 1 | 17-2 | 15-4 | 14-0 | 12-6 |
| 2x10 No. 2 | 17-2 | 15-4 | 14-0 | 12-6 |
| 2x10 No. 3 | 13-5 | 11-7 | 10-7 | 9-5 |
| 2x12 Select Structural | 21-5 | 19-6 | 18-4 | 17-0 |
| 2x12 No. 1 | 20-7 | 17-10 | 16-3 | 14-6 |
| 2x12 No. 2 | 20-7 | 17-10 | 16-3 | 14-6 |
| 2x12 No. 3 | 15-6 | 13-5 | 12-3 | 11-0 |
Spruce-Pine-Fir, 30 psf live load (sleeping rooms)
| Size and grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|
| 2x6 Select Structural | 11-6 | 10-5 | 9-10 | 9-2 |
| 2x6 No. 1 | 11-3 | 10-3 | 9-7 | 8-11 |
| 2x6 No. 2 | 11-3 | 10-3 | 9-7 | 8-11 |
| 2x6 No. 3 | 9-8 | 8-4 | 7-8 | 6-10 |
| 2x8 Select Structural | 15-2 | 13-9 | 13-0 | 12-1 |
| 2x8 No. 1 | 14-10 | 13-6 | 12-8 | 11-5 |
| 2x8 No. 2 | 14-10 | 13-6 | 12-8 | 11-5 |
| 2x8 No. 3 | 12-3 | 10-7 | 9-8 | 8-8 |
| 2x10 Select Structural | 19-5 | 17-7 | 16-7 | 15-5 |
| 2x10 No. 1 | 18-11 | 17-2 | 15-8 | 14-0 |
| 2x10 No. 2 | 18-11 | 17-2 | 15-8 | 14-0 |
| 2x10 No. 3 | 15-0 | 13-0 | 11-10 | 10-7 |
| 2x12 Select Structural | 23-7 | 21-5 | 20-2 | 18-9 |
| 2x12 No. 1 | 23-0 | 19-11 | 18-2 | 16-3 |
| 2x12 No. 2 | 23-0 | 19-11 | 18-2 | 16-3 |
| 2x12 No. 3 | 17-4 | 15-0 | 13-9 | 12-3 |
- • Clear span, face of support to face of support, one simple span, uniform load. Values rounded down to the inch.
- • Dry service (wood at 19% moisture or less), three or more joists ≤ 24 in o.c. sheathed together (repetitive-member factor 1.15).
- • Modern surfaced lumber: 1½ in thick, 5½ / 7¼ / 9¼ / 11¼ in deep.
- • Computed by CrawlSpace Fixes from published design values with the bending, deflection and shear checks the AWC Span Calculator uses, and spot-checked against it. Design values: American Wood Council, 2018 NDS Supplement, Tables 4A and 4B (Southern Pine values per SPIB grading rules). Verify with your building department.
How far can a 2x8 span?
A No. 2 2x8 at 16 in o.c. spans about 11 ft 9 in–12 ft 9 in under 40 psf, depending on species. Spacing, grade and 30 psf loading change it — find your row above.
How far can a 2x10 span?
A No. 2 2x10 at 16 in o.c. spans about 14 ft 0 in–15 ft 7 in under 40 psf, depending on species. Spacing, grade and 30 psf loading change it — find your row above.
How far can a 2x12 span?
A No. 2 2x12 at 16 in o.c. spans about 16 ft 6 in–18 ft 1 in under 40 psf, depending on species. Spacing, grade and 30 psf loading change it — find your row above.
Existing floor
Check your existing joist
Measure one joist under the problem area. Unknown species or grade? Pick “Unknown” and the tool uses the weakest case.
Your joist, as measured
Clear span (face of support to face of support)
Near the limit
96% of allowable
Allowable span for these inputs: 14 ft 0 in, limited by strength in bending. Yours: 13 ft 6 in.
- Bounce at your span
- About 0.29" of sag under a full design live load (L/563). Stiffer than the L/360 floor limit — bounce is unlikely to come from joist span alone.
- Dry vs damp crawl space
- Allowable span 14 ft 0 in dry, 14 ft 0 in if the wood stays above 19% moisture. Damp wood is weaker and more flexible; rotted wood has lost section and needs an inspection, not a recalculation.
Near the limit is not a failure. Check for notches, rot, point loads and sag before deciding anything.
For checking, not designing: an engineer or the building department decides.
Notched or drilled? Check the cut
Sawn lumber only. I-joists and trusses: only as the manufacturer allows.
For checking, not designing: an engineer or the building department decides.
Why measuring matters.Span charts assume modern surfaced lumber. Many houses built before the 1960s have rough-sawn or full-dimension joists — a “2x8” that really is 2 by 8 inches. If it grades like Southern Pine No. 2, a full 2×8 at 16 in o.c. works out to 14 ft 10 in, against 11 ft 9 in for a modern 2x8 — about 26% more. The catch: old lumber rarely carries a grade stamp, so nobody can say what grade it is without an engineer's judgement. That is why “Unknown” falls back to No. 3.
Within, near or over. Under 90% of the allowable span is within; 90–100% is near the limit; over 100% means the joist is longer than these assumptions allow. None of the three is a verdict on safety — it tells you whether span is a plausible cause of what you feel in the floor.
Bounce vs strength
Strong enough but bouncy? Deflection explained
The L/360 in every span chart is a stiffness limit, not a strength limit.
L/360 means the joist may bend no more than its span divided by 360 under the full design live load — about half an inch on a 15-foot span. It exists to keep floors from feeling springy and to protect finishes like tile, not because the joist would break. For many sizes in the chart it is the limit that sets the span, which is why a floor can be perfectly strong and still bounce.
The checker reports your joist's estimated deflection as L/x. Stiffer than L/480 rarely feels bouncy; near L/360 some people notice movement; below L/360 is likely to feel lively. Bounce is usually improved with solid blocking or bridging between joists, a mid-span beam, or sistering — see bouncy or uneven floors for the other causes to rule out first.
Moisture
Damp crawl space, weaker joists
Lumber design values assume wood at 19% moisture or less. A crawl space that keeps framing wetter than that changes the numbers.
The lumber design standard applies a wet-service factor when wood stays above 19% moisture for long periods: stiffness drops 10%, shear strength 3%, and bending strength 15% for higher-strength pieces. For a Douglas Fir-Larch Select Structural 2x10 at 16 in o.c. that trims the span from 17 ft 4 in to 16 ft 8 in. A Southern Pine No. 2 2x10 stays at 14 ft 0 in: its span is set by bending strength, and its bending value is low enough that the reduction does not apply — but it still bends more. Tick “Damp crawl space” in the checker to see yours.
That factor models damp but sound wood. Rot is different: decayed wood has lost section and strength that no factor captures, and it needs a hands-on inspection. If you are not sure how damp your framing runs, our dew point calculator shows the wood moisture that crawl space air drives toward, and the wood rot guide explains why rot changes the answer.
What happens next
Over span, notched or rotted: what happens next
| What you found | Usual next step | Who decides |
|---|---|---|
| Over span, wood sound | A mid-span beam on posts or a short wall, or sistering a new joist alongside | Engineer or building department |
| Near the limit, floor bouncy | Blocking or bridging; then a mid-span beam if needed | Contractor; engineer if structural |
| Notched or drilled beyond the limits | Sistering or a reinforcement detail at the cut | Engineer — cuts in the wrong place can need a specific repair |
| Soft, rotted or insect-damaged wood | Fix the moisture source first, then sister or replace | Inspection; engineer for widespread damage |
| Sagging along a beam or girder line | The beam or its posts, not the joists, may be the problem | Engineer or building department |
The notch and hole limits most building departments enforce for sawn joists: no notch in the middle third of the span; other notches no deeper than one-sixth of the depth and no longer than one-third of it; end notches over a support up to one-quarter of the depth; holes no bigger than one-third of the depth, at least 2 inches from the top and bottom edges and from any other hole or notch. The checker's cut panel tests a notch or hole against them.
For the repair decisions themselves, see repair vs replace floor joists, floor joist repair, support post and pier repair and sagging floors.
Species and grade
Reading a grade stamp (and when there isn't one)
Modern framing lumber carries a stamp from the grading agency showing the grade (Select Structural, No. 1, No. 2, No. 3), the species group and whether it was dried. Look on the side of a joist near an end with a flashlight. Southern Pine is the usual framing lumber in the Southeast; Douglas Fir-Larch and Hem-Fir dominate in the West; Spruce-Pine-Fir is common in the North.
No stamp — common in older houses, or when insulation or paint covers it — means the grade is unknown. The tool then assumes No. 3, and No. 3 of the weakest species if that is unknown too. Treat that result as a reason to ask a structural engineer, not as an answer.
Limits
What this tool does not tell you
Uniform loads only
No point loads — a cast-iron tub, a piano, a water heater, or a bearing wall above.
Simple spans only
No cantilevers, continuous joists over a middle support, or openings with headers.
Not beams or girders
Beam and girder spans depend on how much floor they carry and where the posts are — see beam and girder repair.
Sawn lumber only
Not engineered I-joists, floor trusses, LVL or steel; use the manufacturer's tables.
Not damage
Rot, insects, cracks and earlier bad repairs change capacity in ways no span table captures.
Your code may differ
Local amendments, older codes and engineered designs govern. This is for checking, not designing.
Related
Related pages
Repair vs replace floor joists
When sistering works and when a joist has to come out.
OpenFloor joist repair
Methods, the quote checklist and what to ask a contractor.
OpenSupport posts and piers
Adding mid-span support under a long or bouncy floor.
OpenBouncy or uneven floors
All the causes of floor movement, not just span.
OpenSagging floors
When a dip points to joists, beams or the foundation.
OpenCrawl space structural repair
When a structural engineer should be involved.
OpenFAQs
Floor joist span: common questions
How far can a 2x10 floor joist span?
At 16 inches on center under the common 40 psf live / 10 psf dead load with an L/360 deflection limit, a No. 2 2x10 spans about 14 ft 0 in (Southern Pine) to 15 ft 7 in (Douglas Fir-Larch). At 24 inches on center that drops to 11 ft 5 in–12 ft 8 in; under bedrooms-only loading (30 psf) it rises to 15 ft 8 in–17 ft 5 in. The chart on this page has every grade and spacing.
How far can a 2x8 floor joist span without support?
A No. 2 2x8 at 16 inches on center spans about 11 ft 9 in to 12 ft 9 in between supports, depending on species, under 40 psf live load. Beyond that it needs a beam or wall underneath, or a deeper joist. Spans are clear spans — face of one support to face of the next.
Does joist spacing matter — 16 or 24 inches?
Yes. Each joist carries the floor halfway to its neighbours, so wider spacing loads every joist more. For a No. 2 2x10 the span falls from about 14 ft 0 in–15 ft 7 in at 16 inches to 11 ft 5 in–12 ft 8 in at 24 inches. Wider spacing also needs thicker subfloor.
Can I notch or drill a floor joist?
Within limits, for sawn lumber. As commonly quoted from IRC R502.8.1: notches no deeper than one-sixth of the joist depth, no longer than one-third of the depth, and never in the middle third of the span; end notches up to one-quarter of the depth; holes no larger than one-third of the depth and at least 2 inches from the top and bottom edges and from other holes or notches. Engineered I-joists and trusses can only be cut where the manufacturer allows. Check the code edition your building department uses.
My joists are over the span in the chart. Is my floor going to fail?
Not necessarily. Span tables include safety margins, and for many sizes the limit is stiffness (how much the floor bends), not strength. An over-span floor is more likely to feel bouncy or sag over time than to break. But combined with sagging, cracks, notches, rot or damp wood, it deserves an inspection — a structural engineer or the building department decides whether it needs work.
Sources
Sources and method
- American Wood Council — Design Values for Wood Construction, 2018 NDS Supplement, Chapter 4, Tables 4A and 4B (reference design values, size, repetitive-member and wet-service factors)
- Southern Pine design values per the Southern Pine Inspection Bureau (SPIB) grading rules, as published in NDS Supplement Table 4B.
- American Wood Council — Span Calculator for Wood Joists and Rafters (method: bending, deflection and shear checks; used here only to spot-check our numbers — 17 cases across all four species match it to the inch)
- ICC Building Safety Journal — CodeNotes: Cutting, Drilling and Notching (IRC R502.8.1 notch limits, 2021 IRC)
- International Residential Code, Section R502.3 (floor joist spans) and R502.8.1 (sawn lumber notching and boring) — the tables your building department applies; not reproduced here.
Last updated: .