Composite Deck Calculator
Works for Trex, TimberTech, Fiberon, Azek, and all composite decking brands. Enter your deck size to get board count, hidden clip count, joists, framing, and footings. No sign-up. No paywall.
Enter deck length and depth to calculate materials.
Results
What do these results mean?
Boards — composite deck boards to buy. Includes a waste factor for your chosen pattern (10% perpendicular, 15% diagonal, 20% herringbone).
Hidden clips — fasteners that slip between boards at each joist intersection. Calculated as rows × joist count. Composite decking uses clips instead of face screws.
Joists — the structural members of your deck frame, spaced at your chosen interval.
Framing LF — total linear footage of all framing lumber (joists + perimeter rim joists/ledgers).
Footings / Concrete — post footings spaced 8 ft along the length of the deck.
Plan View
Not to scale
Shopping List
Enter deck dimensions to generate a shopping list.
Related Calculators
Methodology
How the composite deck calculator works.
Board rows
Rows = ⌈ (depth × 12) ÷ (boardWidth + gap) ⌉. Composite boards default to 5.5" wide with a 0.25" gap, giving one row every 5.75". The waste factor (10–20% depending on pattern) is applied when computing total linear footage.
Hidden clips
Clips = rows × joist count. Each clip sits in the gap between two adjacent boards at every joist crossing. Unlike wood decking, composite systems use hidden fasteners instead of face screws — this is what this calculator outputs.
Joists and framing
Joists = ⌈ (length × 12) ÷ joistSpacing ⌉ + 1. Framing LF = joist LF + 2 × length + 2 × depth (joists plus perimeter rim boards). Footings are placed every 8 ft along the deck length.
Note on composite gaps
Most composite manufacturers specify a 1/4" (0.25") gap for thermal expansion — significantly wider than the 1/8" typical for pressure-treated wood. Always check your specific product's installation guide before laying boards.
Composite Decking
Composite vs. pressure-treated wood.
Composite advantages
- → No annual staining, sealing, or sanding
- → Won't splinter, crack, or warp like wood
- → 25–30 year warranties common (vs 10–15 for treated wood)
- → Uniform color and appearance
- → Resists mold, mildew, and insects
Wood advantages
- → Lower upfront material cost
- → Easier to cut and work with standard tools
- → Can be sanded and refinished to look new
- → Natural appearance preferred by some homeowners
Ready to estimate wood decking instead? Use the wood deck calculator. For the framing under any deck, both calculators use the same joist and footing formulas.
FAQ
Frequently asked questions.
Does this work for Trex decking?
Yes. This calculator works for Trex and all similar composite decking brands (TimberTech, Fiberon, Azek, Deckorators, etc.). Composite boards are typically 1" × 5.5" with a 0.25" hidden-clip gap — those are the defaults. Adjust board width and gap if your brand uses different dimensions.
What is the gap between composite deck boards?
Most composite decking manufacturers specify a 1/4" (0.25") gap between boards. This allows for thermal expansion (composite expands and contracts more than wood) and drainage. Some brands specify different gaps — check your manufacturer's installation guide.
How many hidden clips do I need for composite decking?
Hidden clips = rows × joist count. Each clip sits between two boards at every joist crossing. This calculator computes the exact clip count automatically based on your deck dimensions and joist spacing.
Do composite decks need screws?
No — most composite decking systems use hidden fasteners (clips) rather than face screws. This is both for aesthetics and because face-screwing composite can void the warranty. This calculator shows clip count instead of screws when composite mode is selected.
Is composite decking worth the cost over wood?
Composite typically costs 2–3× more upfront than pressure-treated wood but requires almost no maintenance — no staining, sealing, or sanding. Over a 25-year period, the total cost of ownership is often similar or lower. Factor in your time and local labor costs.
Can I use this for a diagonal composite deck layout?
Yes — select "Diagonal" from the laying pattern dropdown. Diagonal layouts add a 15% material waste factor. Herringbone patterns add 20%. Composite is more expensive per linear foot, so diagonal layouts have a higher material cost.
Can I bookmark my composite deck calculation?
Yes — all inputs are saved in the URL. Bookmark the page or share the link to save your composite deck calculation without creating an account.
What joist spacing should I use for composite decking?
Most composite decking manufacturers require 16" on-center joist spacing for perpendicular installation. For diagonal or herringbone layouts, most require 12" OC. Check your specific product's installation guide — exceeding the span can void the warranty.