Decking for a 12 × 32 ft deck in 5/4 × 6 treated, herringbone layout

5/4 × 6 pressure-treated boards

63× 20 ft

26 rows across 12 ft — 998 linear ft including 20% waste

Boards to buy	63× 20 ft
Linear feet832 ft plus 20% waste	998ft
Rows of decking12 ft ÷ 5.625″ repeat	26rows
Board repeat5.5″ actual width + 0.125″ gap — not the nominal size	5.625in
Deck area12 × 32 ft	384ft²
Joists crossedat 24″ o.c. over 32 ft	17joists
Deck screwstwo per board-joist crossing — about 3 boxes of 350	884screws
Layouttwo cuts on most boards and offcuts that fit nothing	herringbone
Butt joints32 ft run exceeds the 20 ft board — stagger the joints and land every one on a joist	Yes

Deck width: 12 ft
Deck length: 32 ft
Board: 5/4 × 6 treated
Layout: herringbone
Joist spacing: 24 in o.c.

Nominal width is not actual width

This is where board counts go wrong. A 5/4 × 6 treated board measures its real width, and with the gap it needs the repeat is 5.625″ — which is what actually decides the row count.

12 ft of deck at that repeat is 26 rows, and 63 boards once 20% waste for the herringbone layout is added.

Working from the nominal size undercounts by close to a tenth.

The gap is not optional in either direction

Treated lumber is sold wet and shrinks. Composite expands with heat. Gap too tight on composite and it buckles in July; gap too wide on wet treated lumber and by autumn you have gaps that swallow a phone.

Screws

884 — two at every board-joist crossing, across 17 joists. One screw per crossing lets the board cup and lift at the corner, and that is the single most common reason a deck looks tired after two summers.

Read the end grain

Lay boards bark-side up. A board cups away from its bark side, so bark-up sheds water off the crown rather than holding it in a trough.

Butt joints

Where the run exceeds a standard board length, stagger the joints so no two adjacent rows meet over the same joist — and double the joist under every joint. A butt joint on a single joist gives each board about ¾ inch of bearing, which is not enough for either board.

Notes

**Nominal width is not actual width.** A "5/4 ×" board measures 5.5″ across. With a 0.125″ gap the repeat is 5.625″, which is what decides the row count — 26 rows here. Working from the nominal size undercounts by close to a tenth.
Sold wet — it shrinks, so gap it tight at about ⅛″. The gap is not optional in either direction: too tight on composite and it buckles in July; too wide on wet treated lumber and you get gaps you can drop a phone through by autumn.
Herringbone layout, 20% waste — two cuts on most boards and offcuts that fit nothing. Order the full allowance in one go; diagonal offcuts rarely fit anywhere else on the deck.
The 32 ft run is longer than a 20 ft board, so there will be butt joints. Stagger them so no two adjacent rows join over the same joist, and double the joist under every joint — a butt joint on a single joist gives each board about ¾″ of bearing.
Fasten with two screws at every board-joist crossing — 884 screws here. One screw lets the board cup and lift at the corner, and it is the single most common reason a deck looks tired after two summers.
Lay the boards bark-side up if you can read the end grain. A board cups away from the bark side, so bark-up sheds water off the crown instead of holding it in a trough.

Nearby sizes

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