Deck board calculator

Enter your deck size and the boards you plan to buy. You'll get the number of boards, the total linear feet, and the screws to fasten them.

How the math works

The deck width divided by the board width plus the gap gives the number of rows. Each row is as long as the deck, so rows times length gives linear feet, and dividing by the board length gives boards. A 16 by 12 foot deck with 5.5 inch boards needs 26 rows, or 416 linear feet. That's 29 boards of 16 feet with 10% extra.

Picking a board length

When the board length matches the deck length, each row is one piece with no seams, which looks cleaner and wastes less. For longer decks, stagger the joints so they don't line up row to row, and make sure every joint lands on a joist.

How big a gap?

Wood boards usually get a gap of about 1/8 inch, the thickness of a 16d nail, so water drains and boards have room to swell. Wet pressure-treated boards shrink as they dry, so many builders install them tight. Composite boards list the gap they need in the installation guide.

Common questions

How many screws do I need?

Two screws wherever a board crosses a joist is standard. Screws are sold by the pound or by the box, and box labels list the approximate count. Hidden fastener systems use clips instead.

Does joist spacing matter for boards?

Yes. Most wood and composite boards are rated for joists 16 inches apart. Boards laid on a diagonal, and some composites, need 12 inch spacing.

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