Deck Calculator
How many deck boards, joists and screws or hidden clips to buy for a deck of any size.
Decking
- Rows of boards
- 26
- Boards per row
- 1
- Linear feet of decking
- 416 ft
- Deck area
- 192 sq ft
Framing
- Joists
- 13 joists
- Joist length
- 12 ft
- Screws or clips (+5%)
- 710
Cost
- Deck boards
- –
How many deck boards do I need?
Divide the deck's width (across the boards) in inches by the board width plus the gap. That gives the number of rows. Multiply by the boards needed per row (deck length ÷ board length, rounded up), then add about 10%. A 16 × 12 ft deck with 5.5 in boards and 3/16 in gaps needs 26 rows: 29 boards of 16 ft, plus 13 joists and about 710 screws.
Worked example: a 16 × 12 ft deck
- Rows: 12 ft = 144 in. Each row takes 5.5 in + 3/16 in gap = 5.6875 in. 144 ÷ 5.6875 = 25.3, so 26 rows.
- Boards: 16 ft boards span the 16 ft deck in one piece: 26 boards, plus 10% = 29 boards.
- Joists: 16 in on center along 192 in: 192 ÷ 16 = 12 spaces, so 13 joists, each 12 ft long.
- Screws: 2 per board at every joist: 26 × 13 × 2 = 676, plus 5% = 710 screws.
Rows of 5.5 in boards by deck width
With a 3/16 in gap. Multiply by the boards per row for the total before extra.
| Deck width (across the boards) | Rows of boards |
|---|---|
| 8 ft | 17 |
| 10 ft | 22 |
| 12 ft | 26 |
| 14 ft | 30 |
| 16 ft | 34 |
Width in inches ÷ 5.6875, rounded up.
Board length and joints
If your boards are shorter than the deck, each row needs a joint, and every joint has to land on a joist. Stagger joints from row to row so they don't line up. Choosing a board length that matches the deck (16 ft boards for a 16 ft deck) saves cutting and waste. For a 20 ft deck, 20 ft boards avoid joints entirely.
Joist spacing and fasteners
- Joist spacing: 16 in on center is common for homes. Trex says joists go at 12, 16 or 24 in on center depending on the board and the use. Many composite boards need 12 in, especially for diagonal decking.
- Face screws: two per board at every joist.
- Hidden clips: one per board at every joist, and they usually set the gap for you.
What this calculator doesn't cover
This works out the deck surface and joists. Beams, posts, ledger boards and footings depend on span tables, loads and local code. The American Wood Council's free DCA 6 guide covers typical residential deck framing, and most decks need a permit. For the footings, the concrete calculator handles round post holes.
Frequently asked questions
How many deck boards do I need for a 12 × 16 deck?
How many screws do I need for a deck?
How far apart should deck joists be?
How much gap should be between deck boards?
How many linear feet of decking do I need?
Guides
Related calculators
Sources and method
- Trex — six tips for planning a successful deck build — joists at 12, 16 or 24 in on center by board and use
- American Wood Council — DCA 6, Prescriptive Residential Wood Deck Construction Guide — beams, posts, ledgers and footings
Last checked October 12, 2026. How we build and test every calculator: methodology.