How many deck boards do I need?
For a 16 by 12 foot deck using standard 2x6 decking (5.5 in actual width), a 1/8 in gap, and 12 ft stock boards, you need 39 boards, including a 10 percent waste factor for cuts and culled boards.
That is this site's deck calculator's own default example. The full row-by-row arithmetic is below, along with the general formula for your own deck size.
The formula
Decking boards run the length of the deck, laid side by side across its width. The calculator works out how many rows fit across the width, how many linear feet of board that is, and then how many stock-length boards to buy.
Worked example, step by step
A 16 by 12 foot deck, 2x6 decking (5.5 in actual width), a 1/8 in (0.125 in) gap, 12 ft stock boards, and a 10 percent waste factor:
| Deck size | 16 ft long × 12 ft wide |
| Effective board width | (5.5 + 0.125) ÷ 12 = 0.46875 ft |
| Rows across the 12 ft width | 12 ÷ 0.46875 = 25.6, rounded up to 26 rows |
| Linear feet of decking | 26 × 16 = 416 ft |
| Plus 10% waste | 416 × 1.10 = 457.6 ft |
| Boards to buy (12 ft stock) | 457.6 ÷ 12 = 38.13, rounded up to 39 boards |
These are the exact default values shown by the deck calculator, so you can check them against your own screen before running your own deck's dimensions.
What changes the board count
- Board width. A wider board, such as a 2x8 at 7.25 in actual width, needs fewer rows to cross the same deck width, usually lowering the total board count for the same square footage.
- Gap between boards. A wider gap adds to each row's effective width, so fewer rows fit and the total linear footage drops slightly. 1/8 in is a common default for pressure-treated lumber that shrinks as it dries.
- Stock board length. Longer stock boards (such as 16 ft instead of 12 ft) cover more linear feet per board, which can lower the board count, but only if your deck's length uses that length efficiently without excess offcut.
- Waste factor. A straightforward rectangular deck typically uses around 10 percent; diagonal decking, picture-frame borders, or decks with lots of cuts around posts and stairs usually need more.
Frequently asked questions
How many deck boards do I need for a 16 by 12 foot deck?
39 boards, using standard 2x6 decking (5.5 in actual width), a 1/8 in gap, 12 ft stock length boards, and a 10 percent waste factor. The deck's 12 ft width needs 26 rows of boards, each row running the full 16 ft length, for 416 linear feet before waste and 457.6 linear feet after.
How do I work out deck board count for a different size deck?
Divide the deck's width by the board's actual width plus the gap you plan to leave, rounded up, to get the number of rows. Multiply rows by the deck's length to get linear feet. Add your waste percentage, then divide by the stock board length and round up, since you cannot buy a partial board.
Does board width change how many boards I need?
Yes, significantly. Wider boards need fewer rows to cover the same deck width, which usually means fewer total boards, even though each board covers more area. A 2x8 (7.25 in actual) needs fewer rows than a 2x6 (5.5 in actual) across the same width.
How much waste should I add for decking?
10 percent is a common default for straightforward rectangular decks, covering miscuts, culled boards, and trim at the ends of rows. More complex layouts, diagonal decking, or picture-frame borders typically need a higher waste allowance.
Why does the gap between boards matter for the board count?
The gap is added to the board's actual width before dividing into the deck's total width, so a wider gap means each row takes up slightly more space and fewer rows fit, which can lower the board count. A 1/8 in gap is a common default for pressure-treated lumber that will shrink slightly as it dries.