Enter your deck dimensions and board size to calculate exactly how many boards you need, including waste allowance for cuts and defects.
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The number of boards depends on your deck area, board width, spacing, and board length. Divide the deck width by (board width + gap) to get the number of rows, multiply by the deck length divided by board length to get boards per row, then add 10-15% for waste from cuts and defects.
For a simple rectangular deck, allow 10% waste. For angled or diagonal patterns, allow 15%. Multi-level or complex shapes may need 15-20% extra. Waste accounts for cuts, defects, and pattern matching.
The standard gap between deck boards is 1/8 inch (3mm) for composite boards and 1/4 inch (6mm) for pressure-treated wood. Proper spacing allows for drainage and wood expansion.
Boards typically run perpendicular to the joists and across the shorter dimension of the deck. Running boards the long way can reduce seams but may require longer (and more expensive) boards. Diagonal patterns add visual interest but increase waste by 15% or more.
Choose board lengths that minimize waste. If your deck is 16 ft long, 8 ft or 16 ft boards are ideal. For a 20 ft deck, 10 ft or 20 ft boards minimize cuts. Fewer seams means a cleaner look and faster installation.
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