Choose wood species, joist size, and joist spacing to find the maximum safe deck joist span
or check an existing span. Results also show deck load capacity totals using 40 psf live load and 10 psf
dead load assumptions.
Safety warning: This tool uses AWC DCA6 Table 2 joist span and overhang values for a
narrow residential deck use case. It is not a professional engineering assessment and does not approve
a deck for construction or occupancy.
Deck joist span calculator
Feet and inches between support faces, not including overhang.
Feet, for total load estimate.
Feet, for total load estimate.
Results update automatically. Use the button if you prefer a manual refresh.
Span and load result
Maximum joist span:-
Maximum overhang:-
Entered span:-
Margin:-
Select framing details to see the maximum span.
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.
Method and limitations
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.
Deck joist span table
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.
Maximum deck joist spans and allowable overhangs
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"
Understanding deck joist span and load capacity
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.
How to use this calculator
Choose whether you want the maximum joist span or want to check an existing span.
Select the DCA6 species group, joist size, and joist spacing.
If checking an existing deck, enter the span in feet and inches between support faces.
Add deck width and length if you want live, dead, and combined load totals.
Review the span result, margin, overhang limit, decking warnings, and limitations.
1. Live Load (40 PSF)
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.
2. Dead Load (10 PSF)
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.
Critical Failure Points
Ledger Board: Where the deck attaches to the house. It carries a large share of
the deck load and must be properly flashed and bolted. Nails can pull out over time.
Post-to-Beam: A beam sitting on top of a post with a connector is safer than
a side-mounted beam, which places shear on the fasteners.
Rot: Pressure-treated lumber is required for framing, and posts should be rated
for ground contact to prevent decay.
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.
Common deck joist span examples
Can 2x8 joists span 12 feet at 16 inches on center?
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".
How far can a 2x10 deck joist span?
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.
Can my deck support a hot tub?
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.
Deck joist span FAQ
How do I measure deck joist span?
Measure from the face of one support to the face of the next support. Do not include joist overhang beyond the beam.
What does on-center spacing mean?
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.
What are live load and dead load?
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.
Is 12, 16, or 24 inch spacing better?
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.
What does No. 2 lumber mean?
No. 2 is a common structural lumber grade. The DCA6 Table 2 values used here assume No. 2 grade lumber in wet service conditions.
Is snow load included?
Only ordinary residential deck loading is included. DCA6 excludes decks with snow, drift, or sliding snow loads above 40 psf from its prescriptive scope.
Why are hot tubs excluded?
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.
Does composite decking change spacing?
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.
When should I call an engineer?
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.
