Composite Decking Calculator: How Many Boards Do I Need? (2026 Cost Guide)
Wood-plastic composite boards (Trex, TimberTech, Fiberon style) — no staining, sealing or splinters.
Composite decking boards are typically 5.5 inches wide (a nominal 1×6) and sold in 12, 16 and 20 ft lengths. This estimator counts boards based on your deck's dimensions, board width plus the manufacturer's recommended gap, and a waste factor for end cuts. Choose a board length that spans your deck without butt joints whenever possible.
1Measure the space
2Board size & layout
Recommended: 10% for straight/offset, 15% for diagonal & herringbone.
3Packaging & price
Your Composite Decking estimate
Area incl. waste
211.2 sq. ft
boards needed
28
Purchase
28 boards
Material cost
$1,181
- DIY — materials only$1,181
- Installation labor (pro)$1,536 – $3,072
- Hire a pro — total installed$2,717 – $4,253
Labor at $8–$16 per sq. ft (US average). Doing it yourself saves roughly $1,536–$3,072.
Material shopping list
| Composite Decking (5 1/2" × 192")205.3 sq. ft of coverage | 28 boards |
| Hidden fastener boxes (≈ 50 sq. ft each) | 4 boxes |
| Color-matched screws for board endsPlus fascia boards and end caps if needed | 1 box |
192 sq. ft · Straight / Grid · 10% waste. Buy all boards from the same lot.
How many boards do I need? Quick-reference table
Based on 5 1/2" × 192" boards with 3/16" joints and $5.75/sq. ft material. "Straight / Grid" uses 10% waste; diagonal/herringbone uses 15%.
| Size | Area + 10% | boards | boards @ 15% | Material | Installed (pro) |
|---|---|---|---|---|---|
| 10×10 ft (100 sq. ft) | 110 sq. ft | 15 | 16 | $633 | $1,433–$2,233 |
| 12×12 ft (144 sq. ft) | 158.4 sq. ft | 21 | 22 | $886 | $2,038–$3,190 |
| 16×12 ft (192 sq. ft) | 211.2 sq. ft | 28 | 30 | $1,181 | $2,717–$4,253 |
| 20×16 ft (320 sq. ft) | 352 sq. ft | 47 | 49 | $1,982 | $4,542–$7,102 |
| 20×20 ft (400 sq. ft) | 440 sq. ft | 58 | 61 | $2,446 | $5,646–$8,846 |
The composite decking formula, step by step
- Measure the area. Multiply length × width in feet. Measure each section separately and add them for L-shapes.
- Add waste. Add 10% for straight or offset layouts and 15% for diagonal or herringbone.
- Find coverage per board. (board length + joint) × (board width + joint) ÷ 144 = sq. ft per board.
- Count boards. Divide the area including waste by the coverage per board and round up.
- Order full lengths. Order whole boards; choose a length that spans the area to minimize butt joints.
Worked example — a 16 × 12 ft area is 192 sq. ft. Adding 10% gives 211.2 sq. ft. Each 5 1/2" × 192" board with a 3/16" joint covers 7.591 sq. ft, so you need 28 boards.
Composite Decking cost guide (2026)
- Material: $3.50–$9.50 per sq. ft (calculator default $5.75).
- Professional labor: $8–$16 per sq. ft. Labor to install decking boards and fascia over a sound existing frame. A new deck with framing typically runs $25–$45 per sq. ft installed.
- Typical 16×12 project: $1,181 DIY vs. $2,717–$4,253 professionally installed.
Pro tips for composite decking
- Run boards perpendicular to the joists. Standard 16" on-center joists work for straight layouts; diagonal layouts usually need joists at 12" on-center.
- Follow the manufacturer's gap: typically 3/16" side-to-side and 1/8"–3/16" end-to-end depending on temperature at install.
- Pick a board length that matches your deck length (or a multiple) to avoid wasteful short off-cuts.
- Budget for hidden fasteners, fascia boards and end caps — they're sold separately from the deck boards.
Composite Decking FAQ
How many composite deck boards do I need for a 12×16 deck?
With 5.5" boards and a 3/16" gap, a 12×16 ft deck (192 sq. ft) needs about 26 sixteen-foot boards running the 16 ft direction — 28 boards after a 10% waste allowance.
How much does composite decking cost per square foot?
Composite deck boards cost about $3.50–$9.50 per sq. ft of deck surface depending on the brand line, plus $8–$16 per sq. ft for professional installation over an existing frame.
What waste factor should I use for composite decking?
Use 10% for straight layouts and 15% for diagonal or picture-frame layouts, which create many angled cuts.
Can I install composite decking on 24-inch joist spacing?
Most composite boards require 16" on-center joists for residential decks (12" for diagonal installs or commercial use). Check the manufacturer's span chart before ordering.