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Deck board calculator: rows and linear length
Estimate how many rows of decking cross a deck and the linear board length required, with the gap between boards made explicit.
Direct answer
Each row covers its own board width plus one gap. Divide the deck dimension across the boards by that covered width and round up to get rows, then multiply rows by the board run length and add a waste allowance for the linear quantity.
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Formula
Worked example
A 16 ft by 12 ft deck with 5.5 in boards and a 0.25 in gap covers 5.75 in, or 0.479 ft, per row. Twelve feet across needs ceiling(12 / 0.479) = 26 rows. At 16 ft per row with a 10 percent allowance, that is 26 x 16 x 1.1 = 457.6 linear ft of decking, excluding framing, fasteners, stairs, and railings.
Assumptions
- The deck is rectangular and boards run in one direction with no diagonal or picture-frame border.
- Board face width is the actual dressed dimension.
- The gap value is the designed installed gap for the chosen material and moisture condition.
Caveats
- Boards are sold in fixed stock lengths, so linear length must be converted into whole boards.
- Joist spacing, span, ledger attachment, footings, guards, and stairs are structural decisions outside this arithmetic.
- Composite and wood products have different gap, fastener, and span instructions that override a generic default.
Primary references
- Wood Handbook: Wood as an Engineering MaterialUSDA Forest Service, Forest Products Laboratory; accessed 2026-08-02.
- 2024 International Residential Code: Building PlanningInternational Code Council; accessed 2026-08-02.
Understand and continue
Deck framing layout and decking quantities
Lay out joists, beams, and posts for a rectangular deck, then convert the surface into board rows and linear length.
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