Deck board calculator
Deck size, board width, gap and joist spacing: you get boards with waste, joist footage, fasteners and supports.
Purchase quantity
37 board
Net measurement: 129.167 ft² · Waste 10 %
- Deck boards37 board
- Joists / battens119.094 ft
- Clips or fixings (one per crossing)220 unit
- Pedestals or supports (every 20 in)77 unit
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How it's calculated (visible formula)
rows = ceil(width ÷ (board + gap)); boards = ceil(rows × length ÷ board length × (1 + waste)); joists = ceil(length ÷ spacing) + 1
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Measure deck length and width and choose board direction.
- Rows = width ÷ (board + gap).
- Boards per row from board length; total with waste.
- Joists from spacing and their length.
- Add clips or screws (one per crossing) and supports.
Worked example: 13 × 10 ft deck, 5½ in boards × 8 ft, ¼ in gap
- 10 ft ÷ 5.75 in ≈ 21 rows
- 21 × 13 ÷ 8 ≈ 34 → +10% = 38 boards
- 13 ft ÷ 16 in = 10 + 1 = 11 joists
→ About 38 boards, 110 ft of joists and 230 clips.
Common mistakes
- Laying boards tight: wood swells and cups.
- Joists too far apart for composite.
- Setting joists directly on soil.
Pro tips
- Slope the deck about ⅛ in per foot away from the house.
- Use adjustable pedestals on slabs for quick leveling.
- Stagger butt joints and land them on doubled joists.
- Leave ½–¾ in from walls for drainage and movement.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- What gap between deck boards?
- About ⅛–¼ in for wood; follow the maker for composite.
- How far apart are deck joists?
- 16 in on center; 12 in for composite on diagonals.
- Clips or screws?
- Hidden clips leave a clean surface; face screws cost less.
- Wood or composite decking?
- Wood is cheaper and natural; composite needs less upkeep.
- How long does pressure-treated decking last?
- 15–20 years with good drainage and maintenance.
- Can I build a deck on the ground?
- Not directly — it needs a stable, drained base and joists kept off the soil.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.