Composite Decking Calculator
Composite (Trex, TimberTech, Fiberon and the like) uses the same math with a 3/16″ gap, and many brands require 12″ joist spacing for diagonal or heavier boards. Grooved boards use hidden clips instead of screws — about 90 per 100 ft².
Order 29 boards (464 lf) — pick the stock length that leaves the least offcut; 16-footers cover a 16 ft deck in one piece.
- Deck area
- 192 ft²
- Rows @ 5.50″ + 0.188″ gap
- 26
- Boards per row (16 ft stock)
- 1
- Waste 10%
- + 3
- Boards to buy
- 29
- Linear feet of decking
- 464 lf
- Joists @ 16″ o.c. (12 ft span)
- 13
- Screws / hidden fasteners
- ≈ 6.7 lb
- Materials + delivery$14–$65 / board · Sep 2026
- $506 – $1,985
- Installed (with labor)typ. $5,538
- $3,386 – $9,665
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What will this deck job cost?
See the installed price range for these quantities and get up to 3 quotes from local contractors. Free, no obligation.
How to calculate deck by hand
Rows = Width (in) ÷ (board width + gap) · Boards = rows × ⌈length ÷ stock⌉ × (1 + waste) · Joists = length ÷ spacing + 1
Worked example
- Rows: 12 ft × 12 = 144″ ÷ (5.5 + 0.125) = 25.6 → 26 rows.
- Boards per row: 16 ft ÷ 16 ft stock = 1 → 26 boards net.
- Waste 10%: 26 × 1.10 = 28.6 → 29 boards (464 lf).
- Joists: 16 ft ÷ 16″ = 12 + 1 = 13 at 12 ft, plus 2 rim joists · Fasteners: 192 ft² × 3.5 lb/100 ≈ 7 lb of screws.
- 5.5″ boards, ⅛″ gap
- 2.13 rows per ft of width
- Decking per 100 ft²
- ≈ 215 lf of 5.5″ boards
- Screws per 100 ft²
- ≈ 3.5 lb (350 screws)
- Joists @ 16″ o.c.
- 0.75 per ft + 1
Questions crews ask
How many composite boards for a 16x12 deck?
144″ ÷ (5.5 + 0.1875) = 25.3 → 26 rows of one 16 ft board = 26, order 29 with 10% waste. Composite comes in 12, 16 and 20 ft; 20-footers let you run a 16 ft deck without a joint and use the offcuts for stairs.
What joist spacing does composite need?
16″ o.c. for boards laid perpendicular, 12″ for diagonal layouts and for some solid-core boards; stair treads 12″ or less. Check the specific brand’s span table — exceeding it voids the warranty.
How many hidden fasteners for composite decking?
One clip per board per joist — about 90 clips (three boxes of 30) per 100 ft² at 16″ centres, plus starter clips along the first board and face screws for the last board and stairs.