Calculators
Decking Calculator — Boards and Fasteners
Joist count is floor(length ÷ spacing) + 1 — preset uses 16 inches on center on a 12 ft wide by 20 ft long deck. Wet pressure-treated lumber is often laid tight and shrinks; composite and dry wood use a gap (default ¼ inch).
The assumptions block states nominal versus actual dimensions and the gap used.
Adjust width, length, and waste below.
| Item | Area | Size | Buy |
|---|---|---|---|
| Deck boards | — | 572 linear ft | 48 boards |
| Deck screws | — | 832 screws | 832 screws (~9 lb boxes) |
Assumptions
- Deck size: 144 in wide × 20 ft long
- Board: 5/4×6 or 2×6 (lays at 5.5 in actual), 12 ft long
- Gap between boards: 0.25 in (composite/dry lumber; lay pressure-treated tight if wet)
- Waste factor: 10%
- Rows across width: 26
- Joist spacing: 16 in on center (16 joists)
- Screws: 2 per board per joist crossing
- Estimates only. Check the coverage figure on your product before buying.
Supplies checklist
- Joist hangers and hardware
- Ledger board and lag bolts (attached decks)
- Concrete footings or post anchors
- End-cut sealer (pressure-treated)
- Chalk line and spacer blocks
Estimates only. Check the coverage figure on your product before buying.
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