Deck Calculator
Rows = deck width ÷ (board + gap), rounded up. A 12 × 16 ft deck with 5.5 in boards and a 1/8 in gap takes 26 boards of 16 ft: 416 linear ft and 676 screws. Screws = rows × joists crossed × 2: a 16 ft run on joists 16 in apart crosses 13 joists (AWC DCA 6: 2 screws per joist).
Deck boards to buy
26 boards of 16 ft
26 rows · 416 ft of boards
Estimate only. Check dimensions, loads and local code requirements with a qualified professional before you build.
- Rows across the deck
- 26 rows (1/8 in gap)
- Linear length of boards
- 416 ft
- Boards per row
- 1 (no offcut reused)
- Joists each row crosses
- 13 at 16 in on center
- Deck screws
- 676 screws (2 per board per joist)
Decking only: joists, beams, posts, footings and the ledger follow AWC DCA 6 and your local permit, not this count.
Worked examples
A 12 × 16 ft wood deck
- 12 ft = 144 in; 144 ÷ (5.5 + 0.125) = 25.6, so 26 rows
- 26 × 16 ft = 416 linear ft
- 16 ft = 192 in; 192 ÷ 16 = 12, + 1 = 13 joists
- 26 × 13 × 2 = 676 screws
Result: 26 boards of 16 ft, 416 linear ft and 676 screws.
Checked by the automated test “deck — 12 × 16 ft, 5.5 in boards, 1/8 in gap, joists at 16 in → 26 rows, 416 linear ft, 676 screws”.
The same deck in composite
- 144 ÷ (5.5 + 0.1875) = 25.3, so still 26 rows
- Screws: 26 × 13 × 2 = 676
Result: 26 rows and 676 screws: the wider gap does not change the count on this deck.
Checked by the automated test “deck — composite 3/16 in gap: still 26 rows”.
How it works
Rows = deck width ÷ (board width + gap), rounded up
Linear feet = rows × deck length
Joists crossed = deck length ÷ joist spacing + 1 (a partial bay adds one)
Screws = rows × joists crossed × screws per joist (2)
Boards = rows × (deck length ÷ board length, rounded up) + extra %
Assumptions
- Gap: about 1/8 in between wood boards (AWC DCA 6: “Space decking boards approximately 1/8" apart”) and at least 3/16 in for Trex composite (2022 guide: “The minimum required width-to-width gapping is 3/16"”).
- Screws: two per board at every joist (AWC DCA 6 “2-#8 screws”, Trex “two screws per joist”).
- Boards run at right angles to the joists, and a nominal 6 in board is 5 1/2 in wide. Offcuts are not reused, and no extra is added unless you type it.
- Decking only: no joist, beam, post, footing or span is sized here.
Reference table
| Deck, across × along the boards | Rows, 1/8 in gap (wood) | Rows, 3/16 in gap (Trex) | Screws, 1/8 in gap |
|---|---|---|---|
| 10 × 10 ft | 22 | 22 | 396 |
| 12 × 12 ft | 26 | 26 | 520 |
| 12 × 16 ft | 26 | 26 | 676 |
| 16 × 20 ft | 35 | 34 | 1,120 |
Two screws per board at each joist, as AWC DCA 6 and Trex specify; with one row less, the 16 × 20 ft composite deck takes 1,088.
Before you buy
- Which side is the width. Type as width the side measured across the boards: it sets the number of rows.
- Board lengths. Type the length you will buy; each row is counted in whole boards, offcuts not reused.
- Frame first. Joists, beams and footings come from AWC DCA 6 and your permit, not from this count.
Common mistakes
- Using the wood gap on composite Trex's 2022 guide sets a 3/16 in minimum between boards, half again the 1/8 in AWC gives for wood: use the gap printed in your own board's guide.
- Counting the nominal 6 in width A 6 in board is 5 1/2 in wide: 144 ÷ 6.125 = 23.5 gives 24 rows instead of 26, two rows short on a 12 ft deck.
- One screw per joist AWC and Trex both ask two per board at each joist: one would give 338 screws instead of 676 on a 12 × 16 ft deck.
- Butting board ends tight Trex gaps the ends too: 1/8 in when installed above 40 °F, 3/16 in below, and 1/4 to 1/2 in where a board meets a wall.
- Sizing the frame with this calculator Joists, beams, posts and footings depend on loads, lumber and soil: follow AWC DCA 6 and your local permit.
Frequently asked questions
What is the right deck board spacing?
About 1/8 in between wood boards (AWC DCA 6). Trex's 2022 guide asks at least 3/16 in side to side in any weather, 3/8 in for docks and heavily wooded areas, never more than 1/2 in: follow your board maker's guide.
How many screws per deck board?
Two at every joist the board crosses (AWC DCA 6, Trex). A 16 ft board on joists 16 in apart crosses 13 joists: 26 screws.
How many deck boards do I need?
Divide the deck width by the board width plus the gap and round up: 26 rows for 12 ft with 5.5 in boards and a 1/8 in gap. On a 16 ft deck, that is 26 boards of 16 ft or 52 of 8 ft.
How many deck screws do I need?
Rows × joists × 2: a 12 × 16 ft deck on joists 16 in apart needs 676 screws (26 rows × 13 joists × 2).
Sources
Formula, examples and sources checked on by the Yardstick Math team. How we check our formulas.
- Prescriptive Residential Wood Deck Construction Guide (DCA 6) — American Wood Council, accessed
- 2022 Decking Installation Guide — Trex, accessed