Deck board calculator
Enter the deck size and board dimensions to get quantities with a cutting allowance.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter deck length (along the boards), deck width (across the boards), board width, gap between boards, board length and joist spacing.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Rows = (deck width + gap) ÷ (board width + gap), rounded up. Boards per row = deck length ÷ board length, rounded up. Total = rows × boards per row × (1 + waste). Joists = deck length ÷ joist spacing (rounded down) + 1. Screws = rows × joists × 2.
Example
Inputs: Deck length (along the boards) = 4 m, Deck width (across the boards) = 3 m, Board width = 140 mm, Gap between boards = 5 mm, Board length = 3.6 m. Result: Boards incl. waste: 47; Board rows: 21; Linear meters of decking: 84 m.
Limits and caveats
- For a rectangular deck with boards along the length; diagonal layouts need more waste.
- Screw count is approximate; hidden fastening systems use clips in different numbers.
Questions about this tool
How big a gap between boards?
Commonly 3 to 6 mm for drainage and movement; composite boards have a gap set by the maker.
What joist spacing is usual?
Often 400 mm for thinner and composite boards and 600 mm for some thicker boards; follow the maker instructions.
Why 10% waste?
End trimming, swapping defective boards and staggering joints all use up some material.