Deck Material List Calculator
Enter the deck length and width, joist spacing, and deck board width, and this deck material list calculator counts every decking board, joist, rim joist, support post, and box of screws — waste already included.
Board count includes 10% waste. Each board is assumed to run the full deck length.
Estimates only — not financial advice. This calculator gives approximate figures for planning. It is not financial, tax, or legal advice; check with a qualified professional before making decisions.
How the deck material list calculator works
Decking boards run across the joists, so the board count is the deck width in inches divided by the board width, rounded up, plus 10% waste for cuts and defects. Each board runs the full deck length — if your boards come shorter than the deck is long, you will need to butt joints and the count rises.
Joists run the deck length at your chosen spacing: 16 inches on center is standard for residential decks, 12 inches for diagonal decking or heavy loads. Two rim joists cap the ends, support posts land roughly every 8 ft, and screws run two per board-joist crossing, sold by the 100-count box.
boards = ⌈(W × 12) / b⌉ × 1.1 · joists = ⌈(L × 12) / s⌉ + 1 · posts = ⌈L / 8⌉ + 1
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Deck material list calculator FAQ
How many deck boards do I need?
Divide the deck width in inches by the board width and round up, then add 10% waste. A 20 ft wide deck with 5.5-inch boards needs ⌈48 × 5.5⌉ × 1.1 ≈ 48 boards, each as long as the deck.
12 vs 16 inch joist spacing: which should I use?
16 inches on center is standard for straight-laid residential decking. Use 12 inches for diagonal decking, heavy hot tubs, or a stiffer feel — it adds about a third more joists.
How many deck screws do I need?
About two screws per board-joist crossing: boards × joists × 2. A 320 sq ft deck typically needs 1,500–2,500 screws, which is 15–25 boxes of 100.
How many footings does a deck need?
Roughly one support post every 8 ft of deck length, so a 16 ft deck needs 3 posts — each on its own concrete footing. Wider decks and stairs add more.
What waste factor should I use for decking?
10% is the standard allowance for cuts, splits, and cull boards. Use 15% for diagonal layouts or decks with lots of angles, since angled cuts waste more stock.