Deck board calculator
How many deck boards, joists and screws a deck needs, for wood or composite boards of any length.
Deck boards
- Rows of boards
- Joists
- Deck screws
- Deck area
How to use it
- Enter the deck's length in the direction the boards run, and its width across the boards, both in feet.
- Enter the board's actual width. Most 5/4 × 6 and 2 × 6 deck boards are about 5.5 inches wide; check composite boards' labels.
- Set the gap between boards and the board length you'll buy.
- Choose your joist spacing.
The calculator shows how many boards to buy, the number of rows, joists, and roughly how many deck screws you'll use.
How it's calculated
| Item | Formula |
|---|---|
| Rows of boards | width in inches ÷ (board width + gap), rounded up |
| Linear feet | rows × deck length × (1 + extra) |
| Boards | linear feet ÷ board length, rounded up |
| Joists | length in inches ÷ joist spacing, rounded down, + 1 |
| Screws | 2 per board at every joist |
A 16 × 12 ft deck with 5.5 in boards and 1/8 in gaps has 26 rows. With 10% extra that's about 458 linear feet: 29 boards at 16 ft, or 46 at 10 ft.
Choosing board length
- Boards that span the whole deck in one piece look best and waste the least. A 16 ft deck uses 16 ft boards with no joints at all.
- Where boards must join, every joint has to land on a joist. Stagger the joints from row to row so they don't line up.
- Shorter boards waste more. A 12 ft deck built from 8 ft boards leaves a 4 ft offcut on many rows. The 10% extra covers some of this, but plan the layout before buying.
Joist spacing
16 inches on center is standard for most wood decking. Many composite and PVC boards, and boards laid diagonally, need 12 inches. Check the board maker's installation guide, because using the wrong spacing can void a composite board's warranty.
Tips
- Gaps: wet pressure-treated wood shrinks as it dries, so it's often laid tight with no gap. Dry wood and composite usually get a gap of about 1/8 to 1/4 in, as the manufacturer specifies.
- Fasteners: use screws or hidden fasteners rated for your board type and for treated lumber.