Deck Board Calculator
Enter the deck size and board details. Boards are assumed to run along the deck's length, across the joists.
- Tested formulas
- Feet or metric
- Printable shopping list
2 What to buy
Updates as you type| Deck area | 192 sq ft |
|---|---|
| Board rows | 26 |
| Boards per row | 1 (no joints) |
| Linear feet of decking | 416 ft |
| Hidden fastener clips (alternative) | 338 |
| Joist hangers | 26 |
Shopping list
Quick answer
A 16 × 12 ft deck with 5½-inch boards and 3/16-inch gaps needs 26 rows: 29 boards 16 ft long with 10% extra, 13 joists at 16 inches on center, and about 676 deck screws.
Boards for common deck sizes
| Deck | Board length | Boards | Joists | Screws |
|---|---|---|---|---|
| 10 × 10 ft | 10 ft | 25 | 9 | 396 |
| 12 × 12 ft | 12 ft | 29 | 10 | 520 |
| 16 × 12 ft | 16 ft | 29 | 13 | 676 |
| 16 × 16 ft | 16 ft | 38 | 13 | 884 |
| 20 × 16 ft | 20 ft | 38 | 16 | 1,088 |
| 20 × 20 ft | 20 ft | 48 | 16 | 1,376 |
5½" boards with 3/16" gaps, joists 16" on center, 10% extra. Use the calculator above for your exact size.
How many deck boards do I need?
Count rows, not square feet. Each row covers one board width plus one gap, so rows = deck width ÷ (board width + gap), rounded up. Then multiply by how many boards it takes to span the length of each row. Square-foot shortcuts over- or under-buy because they ignore board lengths and gaps.
Worked example: 16 × 12 ft deck
- Rows: 144" ÷ (5.5" + 3/16") = 26 rows
- One 16 ft board per row, + 10% waste = 29 boards
- Joists at 16" o.c. along 16 ft: 13 joists
- Screws: 26 rows × 13 joists × 2 = 676 screws
Pick board lengths to avoid joints
If your deck is 15 ft long, buy 16 ft boards. Running boards full length looks better and saves labor. On longer decks, plan a staggered or breaker-board pattern so butt joints always land on a joist, ideally a doubled joist, with each board end supported.
Joist spacing
| Decking | Max joist spacing (straight) | Diagonal |
|---|---|---|
| 5/4 wood boards | 16" | 12" |
| 2× wood boards | 24" | 16" |
| Composite / PVC | 16" (often 12" on stairs) | 12" |
Joist size depends on span, species and load. Use a span table (like the DCA 6 guide) or your local code before you buy joists.
Frequently asked questions
How many deck boards do I need for a 12×12 deck?
With 5½" boards and a 3/16" gap you need 26 rows. Using 12 ft boards that is 26 boards, or about 29 with 10% waste.
How many screws per deck board?
Two screws at every joist. A 16 ft board over joists 16" o.c. crosses 13 joists, so 26 screws per board.
Should deck boards be gapped?
Yes. Wet pressure-treated boards can be butted tight because they shrink as they dry. Kiln-dried and composite boards need the gap the manufacturer specifies, usually 3/16" to 1/4".
Last reviewed 2026-10-21. See how we calculate for our sources and assumptions.