Structural timber reference

Deck Joist Span Table

Find maximum deck joist spans for common 2×6, 2×8, 2×10, and 2×12 No. 2 lumber at 12, 16, and 24 inches on center. You can also enter a required clear span to find the smallest listed joist that meets the selected species and spacing.

Reference 2024 IRC §R507.6 Grade No. 2 Load 40 psf live + 10 psf dead Deflection L/360 main span
Use the table only for matching conditions. Species group, grade, spacing, load, treatment/incising assumptions, decking limits, local amendments, and the rest of the deck load path still matter.

Interactive lookup

Find a Deck Joist Size for Your Span

Choose the lumber species group and joist spacing, then enter the clear supported span. The result returns the smallest listed joist whose maximum span is at least the required span.

No. 2 grade. Species-group footnotes differ; review the source notes below.
Decking may require closer spacing than the joist span table permits.
ft
in

Measure the clear supported joist span between the applicable support faces. Do not enter total board length or include the cantilever beyond the beam.

Smallest listed joist 2×8 For the selected species and spacing
Maximum listed span 11 ft 10 in Matched joist row
Required span 10 ft 0 in Clear supported span
Remaining margin 1 ft 10 in Listed maximum minus required span
Why this result: 2×6 is limited to 9 ft 0 in; 2×8 is listed at 11 ft 10 in and is the first listed size that meets a 10 ft 0 in span.

Quick reference

Deck Joist Span Table — 12, 16, and 24 Inches On Center

The tables below show the 40 psf live-load rows for common No. 2 lumber species groups. Select a species above to highlight its table, and select a spacing to highlight the matching column.

Selected lookup Meets entered span Does not meet

Southern Pine — No. 2

Wet-service factor included.

Southern Pine
Maximum allowable Southern Pine No. 2 deck joist spans for the stated 40 psf live-load condition.
Joist size 12 in. o.c. 16 in. o.c. 24 in. o.c.
2×6 1½ × 5½ in. 9′-11″ 9′-0″ 7′-7″
2×8 1½ × 7¼ in. 13′-1″ 11′-10″ 9′-8″
2×10 1½ × 9¼ in. 16′-2″ 14′-0″ 11′-5″
2×12 1½ × 11¼ in. 18′-0″ 16′-6″ 13′-6″

Douglas Fir-Larch / Hem-Fir / Spruce-Pine-Fir — No. 2

Wet-service factor and the table’s incising factor included.

DF-L / HF / SPF
Maximum allowable Douglas Fir-Larch, Hem-Fir, and Spruce-Pine-Fir No. 2 deck joist spans for the stated 40 psf live-load condition.
Joist size 12 in. o.c. 16 in. o.c. 24 in. o.c.
2×6 1½ × 5½ in. 9′-6″ 8′-4″ 6′-10″
2×8 1½ × 7¼ in. 12′-6″ 11′-1″ 9′-1″
2×10 1½ × 9¼ in. 15′-8″ 13′-7″ 11′-1″
2×12 1½ × 11¼ in. 18′-0″ 15′-9″ 12′-10″

Redwood / Western Cedars / Ponderosa Pine / Red Pine — No. 2

Wet-service factor included; the table does not include an incising factor for this species group.

Redwood / Cedar / Pine
Maximum allowable No. 2 deck joist spans for the Redwood, Western Cedars, Ponderosa Pine, and Red Pine species group for the stated 40 psf live-load condition.
Joist size 12 in. o.c. 16 in. o.c. 24 in. o.c.
2×6 1½ × 5½ in. 8′-10″ 8′-0″ 6′-10″
2×8 1½ × 7¼ in. 11′-8″ 10′-7″ 8′-8″
2×10 1½ × 9¼ in. 14′-11″ 13′-0″ 10′-7″
2×12 1½ × 11¼ in. 17′-5″ 15′-1″ 12′-4″

Reference conditions and limits

  • Grade: No. 2 lumber with wet-service factor included.
  • Main-span loading shown: 40 psf live load + 10 psf dead load with L/360 main-span deflection.
  • Incising: the Douglas Fir-Larch / Hem-Fir / Spruce-Pine-Fir group includes the table’s incising factor; the Redwood / Western Cedars / Ponderosa Pine / Red Pine group does not.
  • Not shown: higher snow/live-load rows, cantilever-by-back-span values, other species/grades, engineered lumber, or project-specific structural design.
  • Decking: joist structural span does not override a tighter joist-spacing requirement from the decking provisions or manufacturer.

Measurement diagram

How Deck Joist Span Is Measured

The supported span and the cantilever are different dimensions. Measure the supported joist span between the applicable support faces; do not use the total joist length.

Deck joist supported span and cantilever Side-view framing diagram showing a house or ledger support on the left, a beam near the right, the supported joist span between them, and a separate cantilever beyond the beam. House / ledger Beam Joist SUPPORTED SPAN Required: 10 ft 0 in CANTILEVER
Span ≠ total joist length. The cantilever beyond the beam requires its own check and is not added to the supported span entered in the lookup.

Spacing diagram

What Does 12, 16, or 24 Inches On Center Mean?

On-center spacing is measured from the centerline of one joist to the centerline of the next—not from edge to edge.

Deck joist on-center spacing Top view of three parallel deck joists with centerlines and a dimension arrow showing the selected on-center spacing between adjacent joist centerlines. 16 in. o.c. center center
On center (o.c.) means centerline to centerline. Decking requirements may limit spacing even when the joist itself can structurally span at a wider spacing.

Quick answers

How Far Can 2×6, 2×8, 2×10, and 2×12 Deck Joists Span?

There is no single span for a nominal joist size. Species group and spacing materially change the allowable span, so use the matching row and column rather than a generic rule of thumb.

2×6 deck joist span

For Southern Pine No. 2 under the stated 40/10 psf condition, a 2×6 is listed at 9′-11″ at 12 in. o.c., 9′-0″ at 16 in. o.c., and 7′-7″ at 24 in. o.c.

2×8 deck joist span

For Southern Pine No. 2, a 2×8 is listed at 13′-1″ at 12 in. o.c., 11′-10″ at 16 in. o.c., and 9′-8″ at 24 in. o.c.

2×10 deck joist span

For Southern Pine No. 2, a 2×10 is listed at 16′-2″ at 12 in. o.c., 14′-0″ at 16 in. o.c., and 11′-5″ at 24 in. o.c.

2×12 deck joist span

For Southern Pine No. 2, a 2×12 is listed at 18′-0″ at 12 in. o.c., 16′-6″ at 16 in. o.c., and 13′-6″ at 24 in. o.c.

Using the table

How to Read a Deck Joist Span Table

  1. Measure the clear supported span.Use the applicable distance between support faces; do not use overall joist length.
  2. Identify the lumber species group and grade.Use the grade stamp or approved documentation. Do not transfer a span from one species group to another.
  3. Confirm the on-center spacing.The table provides 12, 16, and 24 in. o.c. columns, but the decking can require closer spacing.
  4. Use the listed maximum at or above the required span.For the sizing tool, equality passes; values are not extrapolated beyond the table.
  5. Check the rest of the deck.Joist span alone does not size the beam, posts, footings, ledger, hangers, fasteners, lateral connections, guards, stairs, or cantilever.

Design factors

What Controls Maximum Deck Joist Span?

Joist depth

Deeper joists generally have greater bending strength and stiffness, but the listed table value—not a rule of thumb—controls this lookup.

Species and grade

Allowable properties differ by species group and grade. Match the actual lumber identification to the table basis.

Joist spacing

Closer spacing reduces tributary deck area carried by each joist, which is why the 12-in. column generally permits longer spans than the 24-in. column.

Loads

The displayed table is the 40 psf live-load case with 10 psf dead load. Higher snow/live loads and unusual concentrated loads require the appropriate table row or design method.

Exterior service

Deck framing is exposed to moisture, and wet-service and incising assumptions affect the published values for some species groups.

Decking limits

A joist may meet its structural span while the decking still requires a smaller on-center spacing. Always check the decking provisions or manufacturer instructions.

Worked example

Example: Size a Joist for a 10-Foot Span

Conditions: Southern Pine No. 2, 16 in. o.c., 40 psf live + 10 psf dead, L/360 main span.

The 2×6 maximum is 9′-0″, which is shorter than the required 10′-0″. The 2×8 maximum is 11′-10″, so the 2×8 is the first listed joist size that meets the span, leaving 1′-10″ of tabulated span margin.

This check addresses only the joist span condition shown. Verify cantilever, decking, connections, beams, posts, footings, loads, and local code separately.

Limits

When This Deck Joist Span Table Does Not Apply

Use another table or design method when

  • The lumber species or grade is outside the groups shown.
  • The load case is higher than the displayed 40 psf live-load condition.
  • The deck supports a hot tub, roof, masonry feature, large planter, or another unusual/concentrated load.
  • The members are I-joists, LVL, SCL, glulam, or another engineered/proprietary product.
  • The locally adopted code or amendments differ from the reference basis.

Verify separately

  • Joist cantilever and adjacent back-span limits.
  • Decking joist-spacing limits.
  • Bearing, blocking, hangers, ledger attachment, and fasteners.
  • Beam, post, footing, lateral-load, stair, and guard requirements.
  • Preservative treatment, incising, corrosion protection, and decay exposure.

Source and scope

Deck Joist Span Data Basis

The span values displayed on this page are organized from the 40 psf live-load portion of the 2024 IRC Table R507.6 reference structure for No. 2 deck joists. The lookup uses the server-rendered values above as its only numeric source of truth; the JavaScript does not maintain a second span dataset.

For final construction, confirm the code edition and amendments adopted by the authority having jurisdiction and review the official code text or other approved design source.

International Code Council American Wood Council

Questions

Deck Joist Span FAQ

How far can a 2×8 deck joist span?

There is no universal 2×8 span. Under the displayed Southern Pine No. 2 40/10 psf condition, a 2×8 is listed at 13′-1″ at 12 in. o.c., 11′-10″ at 16 in. o.c., and 9′-8″ at 24 in. o.c. Other species groups have different values.

How far can a 2×10 deck joist span at 16 inches on center?

Under the displayed 40/10 psf No. 2 condition, the 16-in.-o.c. maximum is 14′-0″ for Southern Pine, 13′-7″ for Douglas Fir-Larch/Hem-Fir/Spruce-Pine-Fir, and 13′-0″ for the Redwood/Western Cedars/Ponderosa Pine/Red Pine group.

Can deck joists be 24 inches on center?

They can only be spaced 24 in. o.c. when both the applicable structural span provisions and the decking requirements permit it. Many decking products or orientations require closer support spacing.

Does a deck joist cantilever count as part of the joist span?

No. The supported main span and the cantilever beyond the beam are separate dimensions. The cantilever must satisfy the applicable cantilever and adjacent back-span limits.

Can I use a floor joist span table for a deck?

Do not use an interior floor-joist table as a direct substitute for deck framing. Exterior decks have deck-specific loading, service-condition, decking, cantilever, and connection requirements.

Does pressure treatment affect deck joist span?

It can. The table basis includes wet-service assumptions, and incising factors apply to some species groups. Verify the lumber species, grade, treatment, and whether the applicable source value includes an incising adjustment.

Deck Joist Span Table Summary

Measure the supported span correctly, match the actual species group and grade, choose the correct on-center spacing, and use the first listed maximum span that meets or exceeds the requirement. Then verify decking, cantilever, beam and post sizing, footings, connections, unusual loads, and locally adopted code requirements before construction.

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