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joists (deck length long)
Decking Calculator
Enter your deck size, board width and joist spacing to estimate the deck boards, joists and screws you'll need — with a materials cost total. Imperial or metric. Nothing is uploaded.
Your deck
Updates live
Units
Runs the same way as the boards.
Across the boards (joists span this).
Result
What to buy0
deck boards (16 ft)
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deck screws
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rows of decking
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deck area (sq ft)
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lineal ft of decking
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estimated cost
Estimates a rectangular deck with boards run along the length. Add framing, ledger, posts and beams separately.
How the deck estimate works
Boards run along the deck's length, so the number of rows is the deck width divided by each board's covering width (board width + the gap). Multiply rows by the deck length to get the lineal feet of decking, then divide by your chosen board length for the board count — plus a waste allowance for cuts and the odd warped piece. Joists run across the width at your spacing (16" on center is standard), and screws are counted as two at every spot a board crosses a joist. Framing, beams, posts, ledger and footings aren't included — this sizes the decking itself.
How many deck boards do I need?
Deck width ÷ (board width + gap) gives the rows; rows × deck length ÷ board length gives the boards. We add your waste % on top.
How many screws?
About 350 per 100 sq ft as a rule of thumb. This tool counts two screws at every board-over-joist crossing for a closer figure.
Will the boards hold up?
Check spans and deflection first — our sag calculator shows how stiff a board is, and the board foot calculator prices framing lumber.