20×12 deck using 5.5" boards
- Boards ≈ 27
- Deck area = 240 sq ft
construction calculator
Decking Board Calculator
Estimate deck board count and total deck area for standard decking projects.
Results
- Deck area (sq ft)
- 240.00
- Boards needed
- 26.00
How to use this calculator
- Enter deck length and width in feet.
- Enter board width and spacing in inches.
- We calculate deck area and boards needed across the deck width.
- Round up and add waste for cuts and defects.
Inputs explained
- Deck length/width
- Overall deck footprint in feet.
- Board width
- Actual face width of the deck board in inches (measure, do not use nominal).
- Spacing
- Gap between boards in inches (e.g., 0.125–0.25).
How it works
We divide deck width by board width plus spacing to estimate how many boards span the deck.
Include extra boards (5–10%) for cuts, picture framing, or defective pieces.
Formula
Board spacing width = (board width + spacing) / 12 ft\nBoards = ceil(deck width ÷ spacing width)
When to use it
- Estimating deck board quantities before buying lumber or composite boards.
- Comparing board widths/spacing to see count changes.
- Budgeting material with a waste allowance for diagonal or picture-frame layouts.
Tips & cautions
- Add 5–10% extra boards for waste; more for diagonal/picture-frame designs.
- Board widths vary by manufacturer—measure actual width (not nominal).
- If boards don’t span full length, increase waste to cover staggered joints.
- Assumes simple rectangular decks without stairs or picture framing.
- Does not include framing, fasteners, or trim pieces.
- Spacing/width inputs are in inches; convert metric before entering.
Worked examples
Add picture frame border
- Add ~4 boards to cover framing cuts and detailing.
Deep dive
This decking board calculator estimates board count and deck area from deck dimensions, board width, spacing, and waste. Enter your deck size to avoid under-ordering and plan waste for cuts and defects.
Use it for straightforward decks. Increase waste for diagonal layouts or picture framing, and measure actual board widths to keep counts accurate.
FAQs
- Does this include joist layout?
- No, it focuses on surface boards. Use a joist spacing calculator for framing.
- What about board length?
- Assumes boards run the full deck length. If you’re staggering shorter boards, add extra to your order.
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