Board count for a 12×12 deck by board length
5.5-inch boards with 1/8-inch gaps, 10% waste.
| Board length | Boards to buy | Total linear ft | Butt joints? |
|---|---|---|---|
| 12 ft | 29 | 348 ft | None |
| 16 ft | 29 | 464 ft | None — 4 ft offcut per board |
| 20 ft | 29 | 580 ft | None — 8 ft offcut per board |
The highlighted length wastes the least lumber for a 12 ft run. Each 12 ft board gives one full row, so there are no butt joints.
Joists and screws
- At 16 in on center: 10 joists spanning 12 ft, about 520 screws (2 boxes of 350)
- At 12 in on center (composite or diagonal): 13 joists and about 676 screws
Joist size depends on the span, wood species and local code. A 12 ft span is a common size, but confirm joist dimensions with your local building department's span tables.
The math
12 ft × 12 ÷ (5.5 + 0.125) = 25.6 → 26 rows
26 rows × 1.10 waste ÷ 1 row per 12 ft board = 29 boards
Common questions
How many deck boards for a 12x12 deck?
29 boards of 12 ft (5.5-inch width, 10% waste included).
How many joists for a 12x12 deck?
10 joists at 16 inches on center, or 13 at 12 inches.
How many screws for a 12x12 deck?
About 520 deck screws — two per board at every joist.
Want the full method, tips and other sizes? See the deck board calculator guide.