Deck Board Calculator (Boards Needed)
Calculate how many deck boards you need based on area, board size, and gap spacing.
What this calculates
Deck boards come in standard widths (5.5" for 5/4 × 6 or 2×6, 3.5" for 2×4) and run lengths (8-20 ft). Boards are installed with a small gap (1/8 - 1/4 inch) for drainage and expansion. This calculator estimates board count and total linear footage including a waste allowance.
Formula & how it works
Effective width = board_width + gap. Rows = ceil(deck_width / effective_width). Boards per row = ceil(deck_length / board_length). Total = rows × boards/row × (1 + waste).
Worked example
12 × 16 deck, 5.5" boards with 1/8" gap, 16 ft length, 10% waste. Effective width 5.625". Rows = ceil(144 / 5.625) = 26. Boards/row = 1. Total = 26 × 1 × 1.10 = 29 boards.
Frequently asked questions
Composite vs wood?
Composite (Trex, TimberTech) is dimensionally similar but expensive. Same calculation works for both.
Diagonal layout?
Add 15% waste instead of 10% — extra cuts.
Joist spacing?
Wood deck: 16" on center. Composite: 12" on center per most manufacturer specs.
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