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Deck Board Calculator

Calculate deck boards, joists and screws for any deck size, for wood or composite decking projects.

Deck boards

Enter the deck size. Results update live.

Boards needed
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Enter the deck size to see the material list.

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How board rows are counted

Boards run across the deck width, so the number of rows is the deck width in inches divided by the board width plus the gap. Each row spans the deck length, and the total linear footage divided by the board length you buy gives the board count, rounded up.

Joists and fasteners

Joists are spaced 16 inches apart for wood decking and 12 inches for many composites, with one extra joist at each end. Screws are estimated at two per joist crossing, which keeps the count realistic for face screwed decks.

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Deck Board Calc FAQs

How many deck boards do I need for a 12x16 deck?
About 28 boards of 5.5 inch decking in 16 foot lengths, depending on the gap. Enter your exact size above for a precise count.
What gap should I leave between deck boards?
Leave 1/4 inch for pressure treated wood, which shrinks as it dries. Composite decking follows the manufacturer's spacing, usually 3/16 to 1/4 inch.
How far apart should deck joists be?
16 inches on center for standard wood decking. Many composite brands require 12 inch spacing, so check the decking warranty requirements.
Should boards run parallel or perpendicular to the house?
Boards usually run perpendicular to the joists, and joists usually run out from the house ledger. That means boards typically run parallel to the house.
How many screws do I need for a deck?
Plan on two screws per joist crossing per board. A 200 square foot deck typically needs around 1,000 screws, and the calculator works it out from your layout.
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