Quantity · Composite decking
Composite / Trex Decking Calculator
Size a composite (Trex-style) deck with profile presets, brand-typical gaps, max joist spans, and hidden-clip counts. This is not a Trex-affiliated bid — confirm every span and fastener on your product’s install guide. For pressure-treated wood takeoffs, use the general decking calculator.
Composite deck details
Most common solid/grooved composite decking face. Gap ~0.1875" · max span 16" straight / 12" diagonal.
Boards parallel to one edge — least waste.
One clip per board at each joist — common for grooved composite.
Boards to buy
58boards
192 sq ft · Standard ~5.5" (Trex-style)
- Joists
- 10 @ 16"
- Clips
- ~260
- Field boards
- 52
- Rough installed
- $5,760–$11,520
Gap ~0.188" · pitch 5.688". Not affiliated with Trex or any brand — match your install guide.
- Pick a composite profile (face + gap + max joist span)
- Field boards from rows × stock length; optional border
- Clips ≈ rows × joists, or face screws from area rate
Price data updated . National US ranges from published supplier and contractor averages. Not a bid. Local quotes vary.
How composite decking quantity is calculated
A profile sets face width, gap, and maximum joist spacing for straight vs diagonal lays. Field boards follow the same row math as wood decking. Hidden clips are estimated as one per board at each joist; face screws use an area rate. Optional picture-frame adds a perimeter stock count.
pitch_in = face_width_in + gap_in board_rows = ceil(width_ft × 12 ÷ pitch_in) boards/row = ceil(length_ft ÷ board_length_ft) field_boards = board_rows × boards/row border_boards ≈ ceil(2 × (L + W) ÷ board_length) (optional frame) boards_buy = ceil((field + border) × (1 + waste %)) joists = ceil(width_ft × 12 ÷ span_in) + 1 clips ≈ board_rows × joists (hidden)
Worked example. A 16 × 12 ft deck on a ~5.5" Trex-style profile with 3/16" gaps (5.6875" pitch) needs ceil(144÷5.6875) = 26 rows. With 12 ft stock: 26 field boards; at 10% waste buy 29. Straight span cap 16" → 10 joists. Hidden clips ≈ 26 × 10 = 260. Rough composite installed for 192 sq ft often lands near $5,800–$11,500.
Composite profile planning chart (Trex-style class)
Generic face widths and span caps used by many grooved composite lines. Your brand’s published chart wins — especially for wide boards and commercial loads.
| Profile | Face | Typical gap | Max o.c. straight | Max o.c. diagonal |
|---|---|---|---|---|
| Standard (Trex-style) | 5.5" | 3/16" | 16" | 12" |
| Narrow | 3.5" | 3/16" | 16" | 12" |
| Wide | 7.25" | 3/16" | 16" | 12" |
- Diagonal / herringbone patterns almost always need tighter joist spacing.
- Solid-edge boards may use face screws instead of clips — switch fastener mode in the calculator.
Hidden clips vs face screws (planning)
Clip count scales with board rows × joists. Face-screw jobs track deck area instead.
| Method | Planning rule | Best for |
|---|---|---|
| Hidden clips | ≈ 1 clip per board at each joist | Grooved-edge composite |
| Face screws | ~350 per 100 sq ft | Solid edge / color-match screws |
| Starter clips | ≈ 1 per joist on first course | Often sold separately — not auto-added here |
Composite / Trex Decking calculator FAQ
- Is this an official Trex calculator?
- No. It is a brand-agnostic composite planning tool that matches common Trex-style board widths and span habits so the “trex decking calculator” query gets a useful answer. Always follow Trex (or TimberTech, Azek, etc.) documentation for your exact SKU.
- How many Trex boards do I need?
- Same geometry as any deck: rows from width ÷ (face + gap), then stock lengths along the run, plus waste. Pick the ~5.5" profile for most Trex Enhance/Select-class boards and enter your deck size.
- How many hidden clips do I need?
- A common planning estimate is one clip wherever a board crosses a joist — roughly board rows × joist count. Starter clips and butt-joint hardware are extra.
- Why did joist spacing change when I picked diagonal?
- Most composite brands reduce maximum on-center spacing for diagonal lays (often to 12"). The calculator applies the profile’s diagonal span cap automatically.
- Does picture-frame double-count boards?
- The border line is a rough perimeter stock estimate on top of the field. Real picture-frame layouts replace some field ends with mitered borders — refine against your cutting diagram.
- Where is the wood decking calculator?
- Use the general decking calculator for pressure-treated and cedar takeoffs with free gap and joist controls.
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