Deck Calculator
Calculate decking boards and joists needed for a deck.
Assumptions used in this calculation
- Board width excludes gap spacing: Uses the board's face width alone, it doesn't add the small gap (typically 1/8 to 1/4 inch) normally left between boards for drainage and expansion, which slightly undercounts real linear footage needed.
- Uniform joist spacing: Assumes joists run at constant on-center spacing across the full deck width, it doesn't add the extra doubled joists typically required at board end-joint seams.
About this calculator
The deck calculator finds the linear feet of decking boards needed to cover a deck's area (with a waste allowance) and how many joists are needed based on standard on-center spacing.
Worked example
16ft × 12ft deck, 5.5in boards, 16in joist spacing, 10% waste
Result: ≈ 461 linear ft of decking, 13 joists
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