Calculate decking boards, joists, posts, and hardware for building a deck.
Divide the deck width by the board width plus a small gap (1/8" or 3 mm), then add 10% for waste and cuts.
16 inches (400 mm) on centre is standard. Some composite decking may allow 12 inch (300 mm) spacing.
Posts are typically placed every 6 feet (1.8 m) in both directions, plus at corners and beam ends.
100 × 100 mm (4×4 in) posts suit most low decks; taller or larger decks often need 150 × 150 mm (6×6 in) posts. Spacing is typically 1.8–2.4 m.
The frame, posts and footings often account for 30–50% of materials. Use our Decking Cost calculator to price the whole build.
Calculate how many deck boards you need based on deck size, board width and the gap between boards.
OpenCalculate the number of deck joists, spacing and total joist length for your decking frame.
OpenWork out how many decking screws you need and how far apart to space them, based on your deck size, board width and joist centres.
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