Deck Boards
Footprint in, lumber list out: rows of boards, the 12-footers to buy, and enough screws to actually hold them.
Your buy list
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twelve-foot boards · 0 screws- Board rows
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- Total linear feet
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- Screw boxes
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Joists at 16" on center assumed — wider spans need thicker boards.
Rows, not square feet
Decks fail when people divide area by area. Boards are discrete: each row consumes one board face (5½ inches on a nominal 2×6) plus its shrink gap, so the deck's short side divided by 5⅝ inches fixes the number of rows — and every row runs the long way, full length, no splices mid-span.
Screws multiply quietly: two at every joist crossing means a modest 12×12 wants around five hundred, or two pounds-plus. Buy the next whole box; the jar in your bench drawer thanks you next spring.
Buy the straight ones
Crown up, cup down, and reject any board bananaed along its edge — the calculator gives you the count, but culling crooked lumber at the store is what makes those rows come out even.
On the counter
The assumptions this calculator ships with — every one is adjustable in the form.
- Board size
- 5.5" face (nominal 2×6) with a 1/8" gap
- Lengths
- Sold as 12 ft boards; the count rounds up
- Screws
- Two per joist crossing, joists at 16" on center
Questions from the aisle
How many deck boards for a 12×12 deck?
With 5.5-inch boards and 1/8-inch gaps laid across the 12-foot width, about 26 rows — and since boards run in 12-foot lengths, that is roughly 26 twelve-footers.
What gap between deck boards?
1/8 inch is standard for pressure-treated lumber, which shrinks as it dries. Composite stays dimensionally stable and most makers call for 3/16 to 1/4 inch — follow the brand card.
How many screws per board?
Two screws at every joist crossing. Joists at 16 inches on center means a 12-foot board crosses ten joists — twenty screws a row, which is how the estimate above builds up.
Should boards run parallel or perpendicular to the house?
Perpendicular to the house, falling away slightly for drainage, and perpendicular to the joists — always. Boards must span joists, never run alongside them.