Deck Calculator

Work out how many decking boards and screws you need for your deck surface, plus the linear feet and an estimate of the cost — waste included.

How to calculate decking

Decking is estimated from the deck's surface area and the size of each board:

Boards = deck area × (1 + waste %) ÷ (board coverage)

Board coverage accounts for the small gap left between boards for drainage and expansion: (board width + gap) ÷ 12 × board length. We add your waste allowance and round up. This covers the visible deck surface — framing is a separate calculation.

Typical board sizes

Nominal sizeActual width
5/4 × 6 (most common)5.5 in
2 × 65.5 in
2 × 43.5 in

Don't forget

  • Framing is separate. Joists, beams, posts, and footings depend on your span and local code.
  • Screws add up. Budget about 3.5 per square foot (two per joist crossing at 16-inch spacing).
  • Diagonal layouts waste more. Add 15%+ for diagonal boards or a picture-frame border.

Frequently asked questions

How many boards for a 12x12 deck?
About 43 boards of 5.5 in × 8 ft decking, including a 10% waste allowance and a 1/8 in gap between boards.
How many screws will I need?
Roughly 3.5 per square foot — about two per board at each joist with joists 16 inches apart.
Does this include joists and framing?
No — it covers the decking boards and screws. Framing is sized separately to your span and code.
How much waste should I add?
10% for straight boards, 15%+ for diagonal layouts or a picture-frame border.

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