REFERENCE TABLE · CONSTRUCTION · DECKS
How far can a deck joist span? For Southern pine No. 2 — the standard treated deck lumber — a 2×8 at 16″ on center spans up to 11′10″ — or 10′1″ if it cantilevers past the beam. Cantilevered joists span less, and most free charts don’t tell you that. This page covers three species groups (Southern pine, Douglas fir-larch / hem-fir / SPF, redwood & western cedars), 2×6 through 2×12, at 12″, 16″, and 24″ on center — with both the no-cantilever and with-cantilever columns, at 40 psf live + 10 psf dead load, wet service. Use the lookup to check any combination, or enter the distance you need to cross and get the smallest joist that clears it.
Pick a species group, joist size, and spacing to get the maximum span — for joists that end at the beam and for joists that cantilever past it. The max cantilever is always 1/4 of the span. Or enter the distance you need to cross — the lookup returns the smallest joist in your species group and spacing that meets it. All values come from the same chart below (NC Residential Code Table AM106.1, No. 2 grade, 40 psf live + 10 psf dead, wet service, L/360).
Match the span to the right column — and make sure it’s the right column. The default lookup: Southern pine 2×8 at 16″ on center, no cantilever → max span 11′10″. Flip the cantilever toggle to yes and the same joist is limited to 10′1″ — a cantilevered joist spans less because it carries its overhang on top of the span. Max cantilever is always 1/4 of the span (the 2:1 back-span rule): 142″ ÷ 4 = 35″ → 2′11″ here. Need 14 ft at 16″, Southern pine, no cantilever? The smallest joist that clears it is a 2×10 — its table span is exactly 14′0″, so there is zero margin: most builders would bump to a 2×12 or tighten the spacing to 12″ for 16′2″ of capacity. And species changes everything: a redwood 2×8 at 16″ with a cantilever only reaches 8′6″.
No. 2 grade, wet service (treated lumber), 40 psf live + 10 psf dead load, L/360. NC Residential Code Table AM106.1 (mirrors IRC R507.5). Two span columns per spacing: joists that end at the beam vs joists that cantilever past it — the cantilevered column is the one most free charts omit. Spans are face-of-support to face-of-support and exclude the overhang. These charts print cleanly — use the print button above for a job-site copy.
| Joist size | 12″ OC, no cant. | 16″ OC, no cant. | 24″ OC, no cant. | 12″ OC, w/ cant. | 16″ OC, w/ cant. | 24″ OC, w/ cant. |
|---|---|---|---|---|---|---|
| 2×6 | 9′11″ | 9′0″ | 7′7″ | 6′8″ | 6′8″ | 6′8″ |
| 2×8 | 13′1″ | 11′10″ | 9′8″ | 10′1″ | 10′1″ | 9′8″ |
| 2×10 | 16′2″ | 14′0″ | 11′5″ | 14′6″ | 14′0″ | 11′5″ |
| 2×12 | 18′0″ | 16′6″ | 13′6″ | 18′0″ | 16′6″ | 13′6″ |
| Joist size | 12″ OC, no cant. | 16″ OC, no cant. | 24″ OC, no cant. | 12″ OC, w/ cant. | 16″ OC, w/ cant. | 24″ OC, w/ cant. |
|---|---|---|---|---|---|---|
| 2×6 | 9′6″ | 8′8″ | 7′2″ | 6′3″ | 6′3″ | 6′3″ |
| 2×8 | 12′6″ | 11′1″ | 9′1″ | 9′5″ | 9′5″ | 9′1″ |
| 2×10 | 15′8″ | 13′7″ | 11′1″ | 13′7″ | 13′7″ | 11′1″ |
| 2×12 | 18′0″ | 15′9″ | 12′10″ | 18′0″ | 15′9″ | 12′10″ |
| Joist size | 12″ OC, no cant. | 16″ OC, no cant. | 24″ OC, no cant. | 12″ OC, w/ cant. | 16″ OC, w/ cant. | 24″ OC, w/ cant. |
|---|---|---|---|---|---|---|
| 2×6 | 8′10″ | 8′0″ | 7′0″ | 5′7″ | 5′7″ | 5′7″ |
| 2×8 | 11′8″ | 10′7″ | 8′8″ | 8′6″ | 8′6″ | 8′6″ |
| 2×10 | 14′11″ | 13′0″ | 10′7″ | 12′3″ | 12′3″ | 10′7″ |
| 2×12 | 17′5″ | 15′1″ | 12′4″ | 16′5″ | 15′1″ | 12′4″ |
Setup: Southern pine 2×8 joists at 16″ on center, no cantilever, 40 psf live + 10 psf dead.
Line 1 — look up the span. The Southern pine / 2×8 / 16″ cell in the no-cantilever column reads 11′10″ — the maximum distance between supports. The with-cantilever cell for the same joist reads 10′1″: one joist, two legal spans, depending on whether it overhangs the beam. Span longer than the right cell and the joist fails the prescriptive table, full stop.
Line 2 — the cantilever. Rule: cantilever ≤ 1/4 of the actual adjacent joist span (the 2:1 back-span rule) — not the “1/3 rule” some sites quote; the IRC says 1/4. 142″ ÷ 4 = 35″ → 2′11″ max overhang past the beam. And the spans above exclude the overhang — they run face-of-support to face-of-support. (Table footnote: cantilevers not exceeding the joist’s nominal depth — 8″ for a 2×8 — are permitted regardless.)
Branch — a different cell: Southern pine 2×10 at 12″, no cantilever → 16′2″. The same joist with a cantilever is limited to 14′6″ — a foot and eight inches lost to the overhang.
Branch — a different species: redwood 2×8 at 16″ with a cantilever → 8′6″ — three feet less than the Southern pine equivalent. Beautiful wood, weaker joist: always check your own species column.
Branch — sizing from a required span: you need to cross 14 ft at 16″ on center, Southern pine, no cantilever. Walk up the 16″ no-cantilever column: 2×6 = 9′0″ (no), 2×8 = 11′10″ (no), 2×10 = 14′0″ (yes). The answer is the smallest that clears: 2×10 — and on your actual 14-ft span you may cantilever up to 14 ÷ 4 = 3′6″.
| Output | Formula | What it means |
|---|---|---|
| Max span (no cantilever) | Table lookup: species × size × spacing, no-cantilever column | 11′10″ for Southern pine 2×8 at 16″ — the longest support-to-support distance the prescriptive tables allow when joists end at the beam. |
| Max span (with cantilever) | Same lookup, with-cantilever column | 10′1″ for the same joist — the span shrinks because the joist also carries its overhang. |
| Max cantilever | ⌊span ÷ 4⌋ (the 1/4 rule) | 2′11″ on a 142″ span; 3′6″ on an actual 14-ft span — never more than the tabulated overhang, and sub-nominal-depth cantilevers are always permitted. |
| Smallest size for a required span | min size with table[size][spacing][column] ≥ needed | 2×10 for 14 ft at 16″, Southern pine, no cantilever — the cheapest compliant joist for the job. |
Spans are from NC Residential Code Table AM106.1 (which mirrors IRC R507.5): No. 2 grade, wet service (treated lumber outdoors), 40 psf live + 10 psf dead load, L/360. Three species groups are tabulated; the Douglas fir-larch / hem-fir / SPF column includes the incising factor for treated lumber. Cantilevered joists use the shorter with-cantilever column; the cantilever itself is limited to ≤ 1/4 of the actual adjacent joist span (the 2:1 back-span rule), and cantilevers not exceeding the joist’s nominal depth are permitted. Spans run face-of-support to face-of-support and exclude the overhang. These tables do not cover higher grades, dry-service conditions, heavy hot tubs or outdoor kitchens, or snow loads — those need engineering. Local code and your inspector have the final word — some jurisdictions amend the tables. This is reference math, not engineering advice.
Bright Side Kit. "Deck Joist Span Chart: Max Span by Size | Bright Side Kit." https://brightoolbox.com/deck-joist-span-chart/ Accessed October 24, 2026.Data sourcesBecause a cantilevered joist spans less. The same Southern pine 2×8 at 16″ reaches 11′10″ when it ends at the beam but only 10′1″ when it cantilevers past it — the overhang loads the joist, so the code shortens the span. Most free span charts publish only the no-cantilever column and never say so. If your joists overhang the beam, use the with-cantilever column or your deck is under-designed.
One quarter of the actual adjacent joist span — no more. This is the 2:1 back-span rule: at least twice as much joist must stay back over the support as sticks out past it. The “1/3 rule” quoted on some sites is wrong under the IRC; the code says 1/4. One exception in the table footnote: a cantilever not exceeding the joist’s nominal depth (6″ for a 2×6, 8″ for a 2×8, and so on) is always permitted. And the overhang itself is never counted in the span.
No. Every span on this page runs face-of-support to face-of-support — the overhang past the beam is measured separately and checked against the 1/4 rule. If your beam-to-beam span is 14 ft and the joist cantilevers 3 ft past the beam, the “span” for the table is 14 ft, not 17.
psf = pounds per square foot. 40 psf live load is the weight of people, furniture, and anything that moves on the deck; 10 psf dead load is the weight of the deck structure itself (joists, decking, rails). Code requires the joists to carry both at once, with safety margin.
Wet service. Interior floor tables assume dry lumber; deck joists live outdoors, and wet lumber is weaker — the tables derate it (the “wet service factor”). That’s why the same 2×8 spans farther in your living room than on your deck.
Check the stamp on the board’s end. Three groups, strongest to weakest: Southern pine, then Douglas fir-larch / hem-fir / SPF (treated SPF is derated by the incising factor — the little slits that let preservative in weaken it), then redwood, western cedars, ponderosa pine, red pine. The gap is real: a Southern pine 2×8 at 16″ with a cantilever spans 10′1″; the redwood equivalent spans 8′6″.
Both: get engineering and a permit. Snow loads add on top of the 40 psf live load, and in heavy-snow regions these tables shrink fast or don’t apply at all — a local engineer or your building department gives you the right number. Most jurisdictions require a permit and inspections for deck framing anyway, and these table values are exactly what inspectors check against. Always confirm locally before you build — this page is a reference, not a permit.