CalcArcade.

Deck Material Calculator

Enter the deck dimensions and the board and joist sizes you plan to use to get a first-pass materials list.

Your numbers

Result

How we calculate it

Boards run along the length. The number of rows is the deck width in inches divided by (board width + gap), rounded up. Linear feet of decking = rows × length, then the waste allowance is added and the total is divided by the board length.

Joists run across the width and are spaced on center. Count = length in inches ÷ spacing, rounded down, plus one. Screws assume two per board-and-joist crossing.

Assumptions and limits

  • Beams, posts, footings, ledger, railing, stairs and hardware are not included.
  • Joist span and beam size depend on lumber species and local building code. Verify with your code or an engineer before building.
  • A standard 5/4 deck board is 5.5 inches wide in practice, even though it is sold as a 6-inch board.

Frequently asked questions

How many deck boards do I need for a 12x16 deck?

With 5.5 inch boards and 1/8 inch gaps, a 12 by 16 foot deck needs 26 rows of boards along the 16 foot length, or about 26 sixteen-foot boards plus waste.

What joist spacing should I use?

Sixteen inches on center is common for residential decks. Composite and diagonal decking often call for 12 inches. Follow the decking manufacturer instructions.

How much waste should I allow?

Ten percent is a common allowance for straight layouts. Diagonal patterns or many cuts can need 15 percent or more.

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Worked example (a fixed example using the starting numbers, it does not change as you type)

Inputs: Deck length (feet) = 16; Deck width (feet) = 12; Board width (inches) = 5.5; Gap between boards (inches) = 0.125; Board length (feet) = 16; Joist spacing, on center (inches) = 16; Waste allowance (%) = 10.

  • Deck boards 29 boards of 16 ft
  • Board rows across 26
  • Linear feet of decking 458
  • Joists (16 in. centers) 13
  • Joist length needed 156 linear ft
  • Deck screws (2 per crossing) 676
  • Deck area 192 sq ft

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Last reviewed: . Formulas and assumptions are described on our methodology page. For information only; not professional advice.