Quantity · Decking
Decking Calculator
Size a rectangular deck in boards, joists, and fasteners from length, width, board face, gap, and stock length. Switch pressure-treated, cedar, or composite for a rough installed band. For Trex-style profiles, hidden clips, and span caps, use the composite decking calculator.
Deck details
Common DIY choice; 16" joist spacing typical for straight lay.
Boards parallel to one edge — least waste.
Boards to buy
58boards
192 sq ft · Pressure-treated wood
- Joists
- 10
- Fasteners
- ~672
- Raw boards
- 52 (26×2)
- Rough installed
- $2,880–$4,800
Pitch 5.625" · Straight lay. Joist count is a planning line — beams, posts, and footings are separate.
- Area = length × width
- Rows = ceil(width × 12 ÷ pitch); boards/row from stock length
- Buy = ceil(raw × (1 + waste %)); joists + fasteners from area
Price data updated . National US ranges from published supplier and contractor averages. Not a bid. Local quotes vary.
How decking quantity is calculated
Boards run the length; rows march across the width at face-width plus gap (pitch). Stock length sets how many boards make one row. Waste covers cuts and culls. Joists are spaced across the width; fasteners scale with deck area.
area_sq_ft = length_ft × width_ft pitch_in = board_width_in + gap_in board_rows = ceil(width_ft × 12 ÷ pitch_in) boards/row = ceil(length_ft ÷ board_length_ft) boards_raw = board_rows × boards/row boards_buy = ceil(boards_raw × (1 + waste %)) joists = ceil(width_ft × 12 ÷ joist_spacing_in) + 1 fasteners ≈ area_sq_ft ÷ 100 × 350
Worked example. A 16 × 12 ft deck with 5.5" boards and 1/8" gaps (5.625" pitch) needs ceil(12×12÷5.625) = 26 rows. With 12 ft stock, one board per row → 26 raw boards; at 10% waste buy 29. Joists at 16" o.c.: ceil(12×12÷16)+1 = 10. Fasteners ≈ 672. Rough PT installed often lands near $2,900–$4,800 for 192 sq ft.
Deck boards per 100 sq ft (before waste)
Assumes boards run the long way and stock is long enough for one piece per row (no end joints). Divide 100 by coverage per board row-foot, or use: rows per foot of width × length factor. Values below are for a 10 ft run depth with full-length stock — scale linearly with area.
| Board / gap | Pitch | Rows / 10 ft width | Boards / 100 sq ft* |
|---|---|---|---|
| 5.5" + 1/8" | 5.625" | 22 | 22 |
| 5.5" + 3/16" | 5.688" | 22 | 22 |
| 5.5" + 1/4" | 5.75" | 21 | 21 |
| 3.5" + 1/8" | 3.625" | 34 | 34 |
| 3.5" + 1/4" | 3.75" | 32 | 32 |
- *For a 10×10 deck (100 sq ft) with stock ≥ 10 ft (one board per row). Shorter stock multiplies boards per row.
- Add 10% waste straight, ~15% diagonal / picture-frame.
Joists across deck width
Planning count = ceil(width × 12 ÷ spacing) + 1. Confirm spans with lumber grade and live-load tables — this is quantity, not engineering.
| Deck width | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 8 ft | 9 | 7 | 5 |
| 10 ft | 11 | 9 | 6 |
| 12 ft | 13 | 10 | 7 |
| 14 ft | 15 | 12 | 8 |
| 16 ft | 17 | 13 | 9 |
Decking calculator FAQ
- How many deck boards do I need?
- Divide the deck width by the board pitch (face width plus gap) to get rows, then multiply by how many stock lengths fit the run. Add 10% waste for straight lays, more for diagonal. This calculator does that math and rounds up.
- What gap should I leave between deck boards?
- Many wood decks use about 1/8" to 1/4" for drainage and swelling. Composite brands specify a gap — follow the clip or fastener instructions. Pick a gap in the calculator to match your product.
- What joist spacing should I use?
- 16" on center is standard for straight residential decking. Diagonal patterns and some composite boards need 12". Always check the span chart for your board thickness and species or brand.
- Does this include posts, beams, and footings?
- No — it sizes deck boards, a planning joist count, and fastener estimate. Framing below the joists and concrete footings are a separate takeoff.
- Is the dollar range a contractor bid?
- No. It is a national installed band for the decking surface (PT, cedar, or composite). Rails, stairs, and site work move the number a lot.
- Where is the Trex / composite calculator?
- Use the composite / Trex decking calculator for profile presets, hidden-clip counts, and composite span caps. This page stays the general wood-or-composite board takeoff.
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