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MyDeckMath

Deck Boards Calculator

Enter your deck's length and width and this calculator tells you how many deck boards to buy, how many rows you'll lay and the total linear footage, including your waste allowance.

10% for straight layouts, 15% for diagonal

Result

  • Deck area192sq ft
  • Boards needed38boards
  • Rows across width35rows
  • Boards per row1boards
  • Total linear footage456lin ft
  • Coverage per board5.63sq ft
  • Deck area (metric)17.8m²
  • Board length (metric)3.66m

How it works

boards = ceil( (length × width) ÷ coverage-per-board × (1 + waste%) )

  1. Deck area = 12 ft × 16 ft = 192 sq ft
  2. Coverage per 12 ft board = (5.5" + 0.125" gap) × 12 ft ÷ 12 = 5.625 sq ft
  3. Boards before waste = 192 ÷ 5.625 = 34.13
  4. With 10% waste = 34.13 × 1.1 = 37.55
  5. Round up = 38 boards

How the deck boards calculator works

Deck boards are sold by length, but you cover area. The bridge between the two is coverage: the face width of the board plus the gap you leave for drainage, multiplied by the board length.

A standard 5/4×6 or 2×6 deck board has an actual face width of 5.5 inches. With the usual 1/8 inch gap, each linear foot of board covers about 0.469 square feet.

Divide your total deck area by the coverage of one board, apply your waste allowance and round up — you can't buy half a board, so always round up, never down.

Formula

boards = ceil( (length × width) ÷ coverage-per-board × (1 + waste%) )

Worked example: a 12 × 16 ft deck

  1. Deck area = 12 ft × 16 ft = 192 sq ft
  2. Coverage per 12 ft board = (5.5" + 0.125" gap) × 12 ÷ 12 = 5.625 sq ft
  3. Boards before waste = 192 ÷ 5.625 = 34.13
  4. With 10% waste = 34.13 × 1.10 = 37.55 → order 38 boards
  5. Rows across the 12 ft width = ceil(144" ÷ 5.625") = 26 rows

Boards needed per 100 sq ft (5.5" boards, 12 ft long)

Deck areaBoards (no waste)Boards (+10% waste)
100 sq ft1820
200 sq ft3640
300 sq ft5459
400 sq ft7178
500 sq ft8998

Calculated with 5.625 sq ft of coverage per 12 ft board (5.5" face width + 1/8" gap).

Frequently asked questions

How many deck boards do I need for a 12×16 deck?

A 12×16 ft deck is 192 sq ft. With standard 5.5" boards 12 ft long you need about 34 boards before waste, or 38 boards with the usual 10% waste allowance. Boards laid 16 ft long reduce row joints and need about 38 boards before waste.

How much waste should I add when ordering decking?

Add 10% for a straightforward rectangular deck with straight cuts. Use 15% for diagonal or herringbone layouts, multi-level decks or boards with known defects. Going above 25% usually means over-ordering.

Should I buy all boards from the same batch?

Yes when you can. Wood and composite boards vary in color and shade between production runs. Buying everything at once, from one lot, avoids visible color mismatch after installation.

How do I account for boards that run across the width instead of the length?

Rotate the inputs: enter the direction the boards run as the deck length and the perpendicular direction as width. The calculator lays rows across the width input, so swap length and width if your layout runs the other way.

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