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Deck Material Calculator

Estimate joists, beams, decking, fasteners and footings for a deck frame.

Deck size

Joists run across the width and land on a beam; decking runs the length.

ft

Along the house, parallel to the ledger.

ft

Out from the house — this is the joist span.

Framing

Checked against the IRC R507 span table for treated southern pine.

Support
ft

Posts get laid out at or under this spacing.

ft

Finished deck surface to grade. Drives post length and guard requirements.

Decking
Decking product

Butt joints have to land on a joist, so longer boards cut waste.

Fastening
10%

10% covers a rectangular deck. Angles, picture framing and stairs need more.

Unit pricing
$/LF
$/ea
$/ea

Concrete pier, post base and the 6×6 post itself.

$/ea
$/100

Per hundred clips or screws.

Estimated material cost

$2,773

192 sq ft of deck, or $14 per square foot in material alone.
Decking boards26 rows at 5.75 in per course
29 × 16 ft
Joists2x10 at 16 in on center
13 × 12 ft
Beam & rim lumber32 LF beam, 56 LF rim and ledger
88 LF
Posts & footingsPosts land 8.0 ft apart
3
Joist hangersOne per joist at the ledger
13
Bill of materials
ItemQuantityUnitUnit costExtended
Joists — 2x10 × 12.0 ft13pieces$23.40$304
Ledger, rim & end joists — 2x1056linear ft$1.95$109
Beam — 2-ply 2x1032linear ft$1.95$62
Composite / PVC — 16 ft boards29boards$62.00$1,798
Posts, bases & footings — 2.0 ft posts3each$145.00$435
Joist hangers13each$1.65$21
Hidden fastener clips390each$0.11$43
Material total$14.44/sq ft$2,773

2x10 at 16 in OC carries the 12.0 ft span

The IRC R507 table allows 14.0 ft for a 2x10 at 16 in on center in No. 2 treated southern pine. Other species and grades span less, so confirm the grade stamp on what you actually buy.

Joist spacing suits the decking product

Composite / PVC is normally rated to 16 in on center for a perpendicular layout. Composite and PVC boards drop to 12 in on center for a diagonal pattern, and most manufacturers void the warranty if the framing is wider than their instructions allow. This is the one decision you cannot retrofit after the frame is built — check the decking installation instructions before you set joists.

The ledger is where decks fail

Deck collapses begin at the ledger connection far more often than anywhere else. Nails are not acceptable. Use through-bolts or approved structural screws in the pattern given in IRC R507.9, flash the ledger properly, and never fasten to brick veneer or to a cantilevered rim joist. At 3.0 ft above grade this deck also needs a guard, and above 30 in a lateral load connection per R507.9.2 applies.

What this assumes

  • Joist spans follow common pressure-treated southern pine values; verify against your local span tables.
  • Composite decking generally requires 16 inch joist spacing, or 12 inch for diagonal patterns.
  • Footing count assumes a standard beam-and-post layout with posts at or under 8 foot centers.

Important

Decks require a permit almost everywhere, and ledger attachment is the single most common cause of deck collapse. Follow the IRC prescriptive deck provisions in R507 or have the connection engineered.

Understanding the result

Joist spacing depends on the decking

Pressure-treated 5/4 decking spans 16 inches comfortably. Most composite decking also requires 16 inch spacing when laid perpendicular, but drops to 12 inches for a diagonal pattern. Check the decking manufacturer's instructions before you frame — it is a cost difference you cannot retrofit.

The ledger is the critical connection

Deck collapses overwhelmingly begin at the ledger. Nails are not acceptable; use through-bolts or approved structural screws in the pattern the IRC specifies, with proper flashing above. Never attach a ledger to a brick veneer or a cantilevered rim.

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