Feet and inches between support faces, not including overhang.
Feet, for total load estimate.
Feet, for total load estimate.
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Assumptions: AWC DCA6 Table 2; 40 psf live load, 10 psf dead load, No. 2 grade, wet service, and L/360 joist deflection. Overhang is limited to the smaller of the table value or one quarter of the actual main span.
Last reviewed: June 9, 2026. This calculator uses the American Wood Council DCA6 Prescriptive Residential Wood Deck Construction Guide Table 2 values for maximum joist spans and allowable overhangs. The table assumes 40 psf live load, 10 psf dead load, No. 2 grade lumber, wet service conditions, and L/360 joist deflection. The guide is based on IRC prescriptive deck provisions, but local amendments and inspection requirements still control your project.
This tool checks only ordinary deck joist span, joist spacing, joist overhang, and simple deck-area design load totals. It does not check beam span, post size, footings, ledger attachment, lateral bracing, guard loads, rot or damage, fastener corrosion, connector selection, local code amendments, snow loads above the DCA6 scope, roofs, hot tubs, masonry, planters, or other concentrated loads.
These values are from AWC DCA6 Table 2 for No. 2 lumber in wet service conditions. Span values are maximum joist spans. Overhang values are table limits and still cannot exceed one quarter of the actual main span.
| Species group | Joist size | 12 in. OC span | 16 in. OC span | 24 in. OC span | 12 in. OC overhang | 16 in. OC overhang | 24 in. OC overhang |
|---|---|---|---|---|---|---|---|
| Southern Pine | 2x6 | 9' 11" | 9' 0" | 7' 7" | 1' 0" | 1' 1" | 1' 3" |
| 2x8 | 13' 1" | 11' 10" | 9' 8" | 1' 10" | 2' 0" | 2' 4" | |
| 2x10 | 16' 2" | 14' 0" | 11' 5" | 3' 1" | 3' 5" | 2' 10" | |
| 2x12 | 18' 0" | 16' 6" | 13' 6" | 4' 6" | 4' 2" | 3' 4" | |
| Douglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir | 2x6 | 9' 6" | 8' 4" | 6' 10" | 0' 11" | 1' 0" | 1' 2" |
| 2x8 | 12' 6" | 11' 1" | 9' 1" | 1' 8" | 1' 10" | 2' 2" | |
| 2x10 | 15' 8" | 13' 7" | 11' 1" | 2' 10" | 3' 2" | 2' 9" | |
| 2x12 | 18' 0" | 15' 9" | 12' 10" | 4' 4" | 3' 11" | 3' 3" | |
| Redwood, Western Cedars, Ponderosa Pine, Red Pine | 2x6 | 8' 10" | 8' 0" | 6' 10" | 0' 9" | 0' 10" | 0' 11" |
| 2x8 | 11' 8" | 10' 7" | 8' 8" | 1' 5" | 1' 7" | 1' 9" | |
| 2x10 | 14' 11" | 13' 0" | 10' 7" | 2' 5" | 2' 7" | 2' 8" | |
| 2x12 | 17' 5" | 15' 1" | 12' 4" | 3' 7" | 3' 9" | 3' 1" |
Deck joist span is the distance a joist can run between supports. For a deck attached to a house, that is usually the distance from the ledger or hanger support to the face of the beam. For a freestanding deck, it is the distance between beam supports. The overhang beyond a beam is separate and must stay within the smaller of the DCA6 overhang table value or one quarter of the main span.
The maximum span changes with lumber species, nominal joist size, and on-center spacing. Larger joists and closer spacing generally increase the allowable span. Decking products also matter: 24-inch spacing can be unsuitable for thin decking, and diagonal or patterned layouts often need closer joists even when the joist span itself is acceptable.
Live load is the weight of people, furniture, movement, and temporary items. The DCA6 joist span table used here assumes 40 pounds per square foot. Snow can control in many regions, and decks with snow, drift, or sliding snow loads above 40 psf need separate design.
Dead load is the weight of the deck structure itself: joists, decking, fasteners, railings, and built-in features. DCA6 Table 2 assumes 10 pounds per square foot. Heavy surface materials, pavers, masonry, built-in kitchens, and large planters can exceed that allowance.
Use this tool to explore ordinary residential framing scenarios like choosing joist size, checking a proposed spacing, or estimating total design load. If your result is close to the limit, or if your deck has unusual loads, tall posts, questionable ledger attachment, visible damage, or a hot tub, consult local building codes and a qualified engineer.
It depends on species. Southern Pine 2x8 joists at 16 inches on center are listed at 11' 10", so 12' is slightly over the DCA6 table value. Douglas Fir-Larch/Hem-Fir/SPF is 11' 1", and the redwood/cedar group is 10' 7".
At 16 inches on center, Table 2 lists 14' 0" for Southern Pine, 13' 7" for Douglas Fir-Larch/Hem-Fir/SPF, and 13' 0" for the redwood/cedar group. At 12 inches on center, each group can span farther.
Do not use this calculator for a hot tub. Water and occupants create concentrated loads far beyond ordinary 40 psf residential deck loading. Hot tubs require a specific design for joists, beams, posts, footings, lateral bracing, and the tub location.
Measure from the face of one support to the face of the next support. Do not include joist overhang beyond the beam.
On-center spacing is the distance from the center of one joist to the center of the next joist. Common deck spacings are 12, 16, and 24 inches on center.
Live load is people, furniture, and movable loads. Dead load is the weight of the deck materials. This calculator uses 40 psf live load and 10 psf dead load.
Closer spacing usually gives a longer allowable joist span and stiffer decking. Sixteen inches is common; 12 inches helps with diagonal or composite decking; 24 inches needs compatible decking products.
No. 2 is a common structural lumber grade. The DCA6 Table 2 values used here assume No. 2 grade lumber in wet service conditions.
Only ordinary residential deck loading is included. DCA6 excludes decks with snow, drift, or sliding snow loads above 40 psf from its prescriptive scope.
Hot tubs create heavy concentrated loads, not just a uniform floor load. They need a project-specific structural design for the tub size, water weight, occupant load, and support layout.
Often yes. Composite and PVC decking products have manufacturer span limits, and diagonal layouts commonly require closer joist spacing such as 12 or 16 inches on center.
Call an engineer for hot tubs, roofs, heavy planters, snow loads, unusual framing, tall decks, visible rot, ledger concerns, or any span that is at or over the table limit.
