EstimatorKitFree joist span reference
Floor joist span chart, and what sets the limit
A No. 2 Douglas fir-larch 2×10 at 16 in on center reaches 15 ft 5 in under a living-area floor, and it is deflection rather than strength that stops it there: the code holds a floor to L/360 of live-load sag, which is half an inch over that distance. This chart carries 1,024 allowable clear spans — four species groups, Select Structural through No. 3, 2×6 to 2×12, at 12, 16, 19.2 and 24 in on center, under both the 40 psf living-area load and the 30 psf sleeping-room load — and marks which of the two checks set every one of them. It is a reference with its assumptions printed beside it, not a verdict: the code your jurisdiction adopted governs, and a joist carrying a wall, a tub or a point load belongs to an engineer.
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- 1,024 spans
- 2×6 to 2×12
- L/360 marked per cell
What every span below assumes
- Use
- Living areas — kitchens, halls, dining and living rooms, stairs, and the floor over a basement
- Live load
- 40 psf
- Dead load
- 10 psf — joists, a plywood or OSB subfloor, one finish floor and a 1/2 in drywall ceiling
- Load per joist
- 40.0 plf live at 12 in; 53.3 plf live at 16 in; 64.0 plf live at 19.2 in; 80.0 plf live at 24 in
- Deflection
- live load only, limited to L/360
- Span
- clear between supports; design span adds 1.5 in of bearing
- Adjustments
- repetitive member ×1.15, size factor by width, dry service
- Assumed
- simply supported, uniformly loaded, uncut section, nothing bearing between supports
Live loads are IRC Table R301.5: 40 psf live load for habitable rooms other than sleeping rooms, 30 psf for sleeping rooms. The 10 psf figure is the dead load the published floor joist tables are printed at, with a second set at 20 psf for heavier assemblies; it moves with what is actually on the joists — a mortar bed under stone runs 15 to 20 psf on its own, and that moves the grid, not the joist. Weigh what is going on the floor before you take the lighter column: a dead load that is 10 psf on the drawing and 20 psf on site shortens a No. 2 2×10 at 16 in on center by well over a foot.
These are allowable spans for the assumptions above and nothing else. No number here is a finding that a floor is safe. A joist carrying a wall, a tub, a stair landing or any point load, one running continuous over a beam, one cantilevered past its support, and anything notched or bored beyond the code limits are all outside the table — the code your jurisdiction adopted governs, and past the edge of the table the decision belongs to an engineer.
| Size | Grade | 12 in o.c. | 16 in o.c. | 19.2 in o.c. | 24 in o.c. |
|---|---|---|---|---|---|
| Douglas fir-larchNDS Supplement Table 4A, visually graded dimension lumber 2 in to 4 in thick | |||||
| 2×6 | Select Structural | 11' 2" | 10' 2" | 9' 6" | 8' 10" |
| 2×6 | No. 1 | 10' 9" | 9' 9" | 9' 2" | 8' 6" |
| 2×6 | No. 2 | 10' 7" | 9' 7" | 9' | 8' 1" |
| 2×6 | No. 3 | 8' 9" | 7' 6" | 6' 10" | 6' 1" |
| 2×8 | Select Structural | 14' 10" | 13' 5" | 12' 8" | 11' 9" |
| 2×8 | No. 1 | 14' 3" | 12' 11" | 12' 2" | 10' 10" |
| 2×8 | No. 2 | 14' | 12' 7" | 11' 6" | 10' 3" |
| 2×8 | No. 3 | 11' 1" | 9' 7" | 8' 9" | 7' 10" |
| 2×10 | Select Structural | 18' 11" | 17' 2" | 16' 2" | 15' |
| 2×10 | No. 1 | 18' 3" | 16' 3" | 14' 10" | 13' 3" |
| 2×10 | No. 2 | 17' 10" | 15' 5" | 14' 1" | 12' 7" |
| 2×10 | No. 3 | 13' 7" | 11' 9" | 10' 9" | 9' 7" |
| 2×12 | Select Structural | 23' 1" | 20' 11" | 19' 8" | 18' 3" |
| 2×12 | No. 1 | 21' 10" | 18' 11" | 17' 3" | 15' 5" |
| 2×12 | No. 2 | 20' 9" | 17' 11" | 16' 4" | 14' 7" |
| 2×12 | No. 3 | 15' 10" | 13' 8" | 12' 5" | 11' 1" |
| Hem-firNDS Supplement Table 4A, visually graded dimension lumber 2 in to 4 in thick | |||||
| 2×6 | Select Structural | 10' 7" | 9' 7" | 9' | 8' 4" |
| 2×6 | No. 1 | 10' 4" | 9' 4" | 8' 10" | 8' 2" |
| 2×6 | No. 2 | 9' 10" | 8' 11" | 8' 5" | 7' 9" |
| 2×6 | No. 3 | 8' 6" | 7' 4" | 6' 8" | 6' |
| 2×8 | Select Structural | 14' | 12' 8" | 11' 11" | 11' 1" |
| 2×8 | No. 1 | 13' 8" | 12' 5" | 11' 8" | 10' 8" |
| 2×8 | No. 2 | 13' | 11' 10" | 11' 1" | 10' |
| 2×8 | No. 3 | 10' 10" | 9' 4" | 8' 6" | 7' 7" |
| 2×10 | Select Structural | 17' 10" | 16' 3" | 15' 3" | 14' 2" |
| 2×10 | No. 1 | 17' 6" | 15' 10" | 14' 8" | 13' 1" |
| 2×10 | No. 2 | 16' 8" | 15' | 13' 8" | 12' 3" |
| 2×10 | No. 3 | 13' 3" | 11' 6" | 10' 5" | 9' 4" |
| 2×12 | Select Structural | 21' 9" | 19' 9" | 18' 7" | 17' 3" |
| 2×12 | No. 1 | 21' 4" | 18' 8" | 17' | 15' 3" |
| 2×12 | No. 2 | 20' 2" | 17' 5" | 15' 11" | 14' 2" |
| 2×12 | No. 3 | 15' 5" | 13' 4" | 12' 2" | 10' 10" |
| Spruce-pine-firNDS Supplement Table 4A, visually graded dimension lumber 2 in to 4 in thick | |||||
| 2×6 | Select Structural | 10' 4" | 9' 4" | 8' 10" | 8' 2" |
| 2×6 | No. 1 | 10' 1" | 9' 2" | 8' 7" | 7' 11" |
| 2×6 | No. 2 | 10' 1" | 9' 2" | 8' 7" | 7' 11" |
| 2×6 | No. 3 | 8' 6" | 7' 4" | 6' 8" | 6' |
| 2×8 | Select Structural | 13' 8" | 12' 5" | 11' 8" | 10' 10" |
| 2×8 | No. 1 | 13' 4" | 12' 1" | 11' 4" | 10' 1" |
| 2×8 | No. 2 | 13' 4" | 12' 1" | 11' 4" | 10' 1" |
| 2×8 | No. 3 | 10' 10" | 9' 4" | 8' 6" | 7' 7" |
| 2×10 | Select Structural | 17' 6" | 15' 10" | 14' 11" | 13' 10" |
| 2×10 | No. 1 | 17' 1" | 15' 3" | 13' 11" | 12' 5" |
| 2×10 | No. 2 | 17' 1" | 15' 3" | 13' 11" | 12' 5" |
| 2×10 | No. 3 | 13' 3" | 11' 6" | 10' 5" | 9' 4" |
| 2×12 | Select Structural | 21' 4" | 19' 4" | 18' 2" | 16' 10" |
| 2×12 | No. 1 | 20' 5" | 17' 8" | 16' 1" | 14' 5" |
| 2×12 | No. 2 | 20' 5" | 17' 8" | 16' 1" | 14' 5" |
| 2×12 | No. 3 | 15' 5" | 13' 4" | 12' 2" | 10' 10" |
| Southern pineNDS Supplement Table 4B, on the design values SPIB reissued in 2013 after re-testing in-grade material; the size factor is not applied because the published values already vary by width | |||||
| 2×6 | Select Structural | 11' | 10' | 9' 4" | 8' 8" |
| 2×6 | No. 1 | 10' 7" | 9' 7" | 9' | 8' 4" |
| 2×6 | No. 2 | 10' 1" | 9' 2" | 8' 4" | 7' 5" |
| 2×6 | No. 3 | 8' 2" | 7' 1" | 6' 5" | 5' 9" |
| 2×8 | Select Structural | 14' 6" | 13' 2" | 12' 5" | 11' 6" |
| 2×8 | No. 1 | 14' | 12' 8" | 11' 11" | 11' 1" |
| 2×8 | No. 2 | 13' 4" | 12' 1" | 11' 1" | 9' 10" |
| 2×8 | No. 3 | 10' 10" | 9' 4" | 8' 6" | 7' 7" |
| 2×10 | Select Structural | 18' 7" | 16' 10" | 15' 10" | 14' 9" |
| 2×10 | No. 1 | 17' 10" | 16' 3" | 15' 3" | 14' 2" |
| 2×10 | No. 2 | 17' 1" | 15' 6" | 14' 2" | 12' 8" |
| 2×10 | No. 3 | 13' 10" | 12' | 10' 11" | 9' 9" |
| 2×12 | Select Structural | 22' 8" | 20' 7" | 19' 4" | 17' 11" |
| 2×12 | No. 1 | 21' 9" | 19' 9" | 18' 7" | 17' 3" |
| 2×12 | No. 2 | 20' 10" | 18' 11" | 17' 3" | 15' 5" |
| 2×12 | No. 3 | 16' 11" | 14' 7" | 13' 4" | 11' 11" |
Δ marks a span that deflection set — the joist ran out of stiffness before it ran out of strength. On the rest, bending under the full load ran out first. 128 of the 256 cells shown carry the mark. Dead load counts against strength but not against the L/360 check, which is why a heavier assembly hands cells back to bending: over the full grid, deflection sets 128 of the 256 cells at 10 psf dead and only 67 of them at 20 psf.
The numbers the spans came from
Fb is shown after the factors that apply to a floor joist — the size factor for its width and the repetitive-member factor at ×1.15. E is the published figure, unadjusted, and it is the only number the deflection check reads.
| Species and grade | Fb, psi | Adjusted Fb at 2×10 | E, psi |
|---|---|---|---|
| Douglas fir-larch — The stiffest of the four groups at every grade, which is why it holds the longest spans on the chart. Sold as DF-L or DougFir west of the Rockies and trucked a long way east of them. | |||
| Select Structural | 1,500 | 1,898 | 1,900,000 |
| No. 1 | 1,000 | 1,265 | 1,700,000 |
| No. 2 | 900 | 1,139 | 1,600,000 |
| No. 3 | 525 | 664 | 1,400,000 |
| Hem-fir — A marketing group rather than a tree: western hemlock plus five true firs, graded together on the weakest of them. Light, clean and easy to nail, and at Select Structural 2×12 it gives up a foot and change against Douglas fir-larch — though at No. 2 the two are within six inches of each other. | |||
| Select Structural | 1,400 | 1,771 | 1,600,000 |
| No. 1 | 975 | 1,233 | 1,500,000 |
| No. 2 | 850 | 1,075 | 1,300,000 |
| No. 3 | 500 | 633 | 1,200,000 |
| Spruce-pine-fir — No. 1 and No. 2 are published as one combined grade, so their rows are identical here — that is the table, not a fault in it. This is the stamp on most of the framing lumber sold through big-box stores. | |||
| Select Structural | 1,250 | 1,581 | 1,500,000 |
| No. 1 | 875 | 1,107 | 1,400,000 |
| No. 2 | 875 | 1,107 | 1,400,000 |
| No. 3 | 500 | 633 | 1,200,000 |
| Southern pine — The species to check twice. The 2013 revision cut the published values hard, so any Southern pine span chart older than that — and there are plenty still online — is optimistic by up to two feet at 2×12. Compare the Fb and E below against the values in force where you are building. | |||
| Select Structural | 1,900 | 2,185 | 1,800,000 |
| No. 1 | 1,250 | 1,438 | 1,600,000 |
| No. 2 | 1,000 | 1,150 | 1,400,000 |
| No. 3 | 600 | 690 | 1,200,000 |
the NDS size factor for visually graded dimension lumber: 1.3 at a nominal 6, 1.2 at an 8, 1.1 at a 10 and 1.0 at a 12 — a deep board bends at a lower stress than a shallow one of the same grade. IRC Table R301.7 limits a floor to a live-load deflection of L/360, checked against the live load on its own; bending is checked against the full live-plus-dead load, and the shorter of the two answers is the span printed. IRC R502.6 requires 1.5 in of bearing on wood, and a span table takes the design span as the clear span plus half of that at each end, which is why a cell here reads about an inch and a half shorter than the raw arithmetic.
64 of 64 rows showing, 256 spans. The CSV carries one line per cell with the Fb, E and the check that governed it, so a takeoff spreadsheet can filter it the same way this page does.
How to read a joist span table without getting caught
The load case comes first, the span second, and what governed the cell tells you which lever to pull.
Set the load case before you read a single number
A span means nothing without the load it was worked out under. Pick the live load first — 40 psf for a living area, 30 psf for a bedroom or an attic floor reached by a fixed stair — then the dead load of the assembly: 10 psf for joists, subfloor, one finish floor and a drywall ceiling, or 20 psf once a mortar bed, a lightweight topping or a plaster ceiling is in the build-up. Moving the dead load from 10 to 20 psf costs a No. 2 Douglas fir-larch 2×10 at 16 in on center a foot and four inches of span, which is the difference between reaching a 15 ft room and not.
Type the clear span, measured between the faces of the supports
Write it any way a tape reads it — 15, 15' 4, 15 ft 4 in, 184 in or 4.7 m all parse. The clear span is the opening the joist crosses, not the outside of the band joists, and the grid works in clear spans because that is the dimension a code table publishes. Every cell that reaches your number is marked, and the panel above the grid names the widest spacing that gets there for each joist size, so you can see what the extra depth buys before you price it.
Read what governed, then check the cell against your own code book
Cells marked with a delta were set by deflection — the joist ran out of stiffness before it ran out of strength — and the rest were set by bending under the full load. That tells you which lever moves the span: a deflection-governed row gets longer with depth or a tighter spacing and barely responds to a better grade, because the modulus of elasticity hardly changes between grades while the bending value collapses. Then take the cell to the adopted code and, where the joist carries a wall, a tub or a point load, to an engineer.
Technical specifications
| Spans on the chart | 1,024 — four species groups, four grades, 2×6 through 2×12 and four spacings, across four load grids |
|---|---|
| Load cases | 40 psf live for living areas and 30 psf for sleeping rooms, each against a 10 or 20 psf dead load |
| Deflection limit | L/360 under live load only: 0.40 in at 12 ft, 0.50 in at 15 ft, 0.85 in at the longest span shown |
| What sets the span | Deflection sets 128 of the 256 cells at 40 psf live over 10 psf dead, and all 64 Select Structural cells; at 20 psf dead only 67 stay deflection-governed |
| Longest span shown | 25 ft 5 in — Select Structural Douglas fir-larch 2×12 at 12 in on center under a 30 psf sleeping-room load |
| Span convention | Clear distance between supports; the design span adds 1.5 in, being half the required bearing at each end |
| Not modeled | Shear, notches and bored holes, a bearing wall or point load overhead, cantilevers, spans continuous over a beam, and wet or fire-retardant-treated service |
| Data kept | None — the filters and the span you type never leave this tab |
Frequently asked questions
How far can a 2×10 floor joist span?
Fifteen feet five inches for a No. 2 Douglas fir-larch 2×10 at 16 in on center under a 40 psf living-area load over 10 psf of dead load. The same joist reaches 17 ft 10 in at 12 in on center and drops to 12 ft 7 in at 24 in, and moving to Select Structural in the same species buys 17 ft 2 in at 16 in while No. 3 gives back 11 ft 9 in. That spread of six feet across one nominal size is why 'how far can a 2×10 span' has no single answer: the size names the section, and the species, the grade, the spacing and the load decide the span.
What does L/360 actually allow a floor to do?
It allows the middle of the joist to drop by the span divided by 360 under live load — 0.40 in over 12 ft, 0.50 in over 15 ft, 0.60 in over 18 ft. Two things about that limit surprise people. It is measured against live load only, so the sag the floor already had when the subfloor went down does not count against it; and it is a serviceability limit inherited from the era of plaster ceilings, written so that a finish would not crack, not so that a floor would feel solid underfoot.
My joists pass the span table and the floor still bounces. Why?
Because a span table limits deflection and says nothing about vibration, and those are different problems. Deflection is how far the floor moves under a static load; bounce is how fast it moves and how long it keeps moving after a footfall, which depends on the mass and the frequency of the whole assembly rather than on one joist's sag. A floor built to the last inch of its tabulated span is at code and can still be unpleasant. What settles it down is depth over spacing — a 2×12 at 16 in beats a 2×10 at 12 in for the same reason a diving board is thin — plus solid blocking at mid-span, a second layer of subfloor glued and screwed rather than nailed, and, on a remodel, sistering rather than adding a beam nobody wants in the basement.
Can I notch or drill a joist for a drain or a cable run?
Within the limits in IRC R502.8 and nowhere near as freely as most people assume. A bored hole may not be closer than 2 in to the top or bottom edge and may not exceed one third of the joist depth; a notch in the top or bottom edge is capped at one sixth of the depth and is not permitted in the middle third of the span; a notch at the end may go to one quarter of the depth. On a 2×10, which is 9.25 in deep, that is a 3 in hole, a 1.5 in edge notch and a 2.3 in end notch. Every span on this chart assumes an uncut section, so a 3 in ABS drain dropped through the middle third of a joist has left the table behind.
Why is Southern pine shorter on a new chart than on an old one?
Because SPIB reissued its design values in 2013 after re-testing in-grade material, and the published spans fell with them — by up to two feet in the deepest sizes. Charts printed before that revision are still circulating and are still wrong, which is the single most common way a Southern pine floor gets ordered short. That is why this page prints the bending value and the modulus of elasticity it used for every species and grade instead of only the answer: compare them against the values in force where you are building, and if they disagree, the values in force win.
Does a tile or stone floor change what I need?
Yes, in both directions at once. The dead load goes up — a mortar bed and stone push a 10 psf assembly to 20, which costs a No. 2 Douglas fir-larch 2×10 at 16 in on center a foot and four inches — and the deflection limit tightens, because the tile industry asks for L/360 under ceramic and L/720 under natural stone against the code's L/360 floor. L/720 is not a stricter reading of the same table; it halves the allowable sag, and no cell on this chart has been checked against it.
Does doubling a joist double its span?
No — it buys about a quarter more span, not twice. Two members side by side carry twice the load at the same distance, which is the case you want under a wall or a tub, but at an unchanged load the span grows as the cube root of stiffness where deflection governs, so doubling the section is a factor of 1.26; where bending governs it is the square root, or 1.41. Depth is the cheaper lever in both cases, because it enters the stiffness cubed: swapping a No. 2 Douglas fir-larch 2×10 at 16 in on center for a 2×12 takes it from 15 ft 5 in to 17 ft 11 in on one board rather than two. Every span on this chart is for a single member.
About allowable spans, L/360, and the gap between bouncy and unsafe
A span table is not a list of measured facts about lumber. It is the printout of two checks run over a grid: the joist has to carry the live and dead load in bending, and it has to keep its live-load sag inside L/360. Whichever check runs out first sets the cell, and the interesting thing is how often that is stiffness rather than strength. At 40 psf live over 10 psf dead, deflection sets exactly half the 256 cells here and every single Select Structural cell, because the modulus of elasticity barely moves between grades — 1,900,000 psi at Select Structural against 1,600,000 at No. 2 in Douglas fir-larch — while the bending value falls from 1,500 psi to 900. Pay for the better grade and most of what you buy is strength you were not short of. Add dead load instead and the balance flips: at 20 psf only 67 of the same 256 cells are still deflection-governed, because dead load counts fully against bending and not at all against L/360. That is the whole reason this chart shows what governed each number rather than only the number.
The assumptions are where floors actually get built wrong. A tabulated span is for a simply supported joist, uniformly loaded, dry, in a repetitive set at 24 in or less with a deck sharing load between members, and with its section uncut. A joist running continuous over a center beam is a different structure; so is one carrying a wall from above, a stair landing framed into its run, a cast-iron tub, or a kitchen island in stone. Notching and drilling quietly break the same assumption: IRC R502.8 caps a bored hole at a third of the depth and no nearer than 2 in to an edge, an edge notch at a sixth of the depth and never in the middle third of the span, and an end notch at a quarter — which on a 9.25 in 2×10 is a 3 in hole, a 1.5 in notch and a 2.3 in end notch, and is a good deal less than a plumber running a 3 in drain would like. Once the size and the spacing are settled, the count of joists you actually buy comes off the run with the linear feet calculator, the toe-nailing and hanger schedule for landing them is on the nail size chart, and the piers or footings under the beam those joists bear on get poured off the concrete calculator.
The last thing worth being clear about is that a bouncy floor and an unsafe floor are not the same complaint, and a span table only addresses one of them. L/360 came out of an era of plaster ceilings and exists so that a brittle finish does not crack; it is a limit on how far the floor moves, not on how it moves. Vibration — the shiver a footfall sends across a room, the glass rattling on a side table — is governed by the mass and the natural frequency of the assembly, which no table in the residential code addresses at all. A floor at the last inch of its span is code-compliant and can still feel awful, and the cures are the ones that add depth and continuity rather than the one that adds grade: a deeper joist, a tighter spacing, solid blocking at mid-span, subfloor glued as well as screwed. None of which changes the boundary this page sits behind. Every number here is an allowable span for a stated set of assumptions, published design values and a calculation anyone can check, and none of them is a finding that a particular floor is safe. Local amendments differ, the adopted edition differs, and the person who signs for a floor outside these assumptions is an engineer.
Where the span you type goes
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The span you enter is compared against a grid compiled into the page itself. There is no lumber yard on the other end of it, no quote request dressed up as a span check, and nothing that remembers what you were building.