How many deck boards for a 8x12 deck?
You need 18 deck boards at 12 ft long.
That is 18 rows across the 8 ft span, or 216 linear feet. Buy 238 linear feet to cover the usual 10% for cuts and defects.
A 8x12 deck by the numbers
| Deck area | 96 sq ft |
|---|---|
| Rows of decking | 18 |
| Board length | 12 ft |
| Boards to buy | 18 |
| Decking | 216 linear ft |
| With 10% waste | 238 linear ft |
| Joists at 16 in on centre | 10 |
| Footings | 6 |
| Deck screws | 480 |
Where that number comes from
- 8 ft across × 12 = 96 in to cover
- 96 ÷ 5.625 = 17.1 rows, rounded up to 18
- 18 rows × 12 ft long = 216 linear feet
- Add 10% for cuts and culls = 238 linear feet
Boards run the length of the deck here, so the 12 ft dimension sets board length and the 8 ft dimension sets how many rows you need. Running them the other way swaps the two numbers.
Working to a different size? The calculator takes any dimensions and returns the same figures.
Cutting a 8x12 out of stock lengths
The 12 ft run lands exactly on a 12 ft board: 18 boards, 18 rows, nothing cut and nothing left over. Why running them the other way changes the order.
Nothing longer divides into 12 ft — the next stock size up is 16 ft, which would leave an offcut too short to use as a row. Buy 18 boards at 12 ft and cut nothing.
Order 238 linear feet, not the bare 216 — about 2 spare rows on a 8x12. What the cull rate covers.
Before you order: getting a decking order right.
Other deck sizes
Deck calculator for any size, or all calculators.