How Many Deck Boards Do I Need? (Common Deck Sizes)
A 20x20 deck takes 86 boards before waste, with 5 1/2 in boards, a gap of 3/16 in and 16 ft stock: 43 rows across, each 2 boards long.
Estimates for planning, not professional advice. Read the full notice.
Work it out for your own sizes
Boards for your own deckExample to try: Across the boards 20 ft, Along the boards 20 ft, Board width 5 1/2 in, Gap between boards 3/16 in
Boards before waste, by deck size and stock length
Boards for a square deck with the board width and gap above, by deck size and by the stock length of the board
| Deck | 8 ft stock | 10 ft stock | 12 ft stock | 16 ft stock | 20 ft stock |
|---|---|---|---|---|---|
| 12x12 deck | 52 | 52 | 26 | 26 | 26 |
| 16x16 deck | 68 | 68 | 68 | 34 | 34 |
| 20x20 deck | 129 | 86 | 86 | 86 | 43 |
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Rows across the deck times the boards in each row, with each row cut from its own boards. The calculator above adds the waste allowance and can share offcuts between rows.
Rows across, by deck size and board width
Rows of boards across a square deck at the gap above, by deck size and board width
| Deck | 3.5 in boards | 5.5 in boards |
|---|---|---|
| 12x12 deck | 40 | 26 |
| 16x16 deck | 53 | 34 |
| 20x20 deck | 66 | 43 |
The widths are examples; use the width of the boards you buy. A narrower board means more rows and more gaps across the same deck.
What changes at a different size
A 12x12 deck is 26 rows across and 26 boards with sixteen foot stock, because each row is one board; at 20x20 each row needs a second board, so the count more than doubles.
Questions
How many boards do I need for a 20x20 deck?
86 boards before waste at the width, gap and stock length in the first sentence. Add your waste allowance in the calculator.
How many deck boards do I need for a 12x12 deck?
The first table gives it for each stock length; a board as long as the deck means one board in each row.
Calculate it for your project
Enter your own sizes to get the amount to buy or the layout figures, with the working shown and a page to print.
Enter your deck in the deck board calculator