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Deck Board Calculator

Number of deck boards and joists for a rectangular deck.

Deck length (along the boards)ftDeck width (across the boards)ftBoard width (actual)inGap between boardsinJoist spacingin

How it's calculated

Boards = deck width in inches ÷ (actual board width + gap), rounded up. Joists = deck length in inches ÷ joist spacing, rounded up, plus one for the end. A 5/4 × 6 deck board is 5½ inches wide; a 3/16-inch gap is common for wood.

Example

A 16 × 12 ft deck in 5½-inch boards: 144 ÷ 5.69 = 26 boards of 16 ft, and 13 joists at 16 inches on center.

Joist spacing for decking

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