Deck Board Calculator
Calculate deck boards, screws and linear feet of lumber for any deck by size, board width and gap.
The deck board calculator returns boards, linear feet of lumber and deck screws for any deck. The math depends on board width (5.5 inches for the standard 5/4x6 or 2x6 - the most common deck board), the gap between boards (3/16 inch is industry standard - allows wood to swell and shrink with moisture) and your board length (12 ft is the most common stock length). Standard waste is 10% for a simple straight-lay deck, 15% for diagonal patterns and 20% for picture-frame or herringbone where every board near the edge gets a custom cut. Screws are 2 per joist per board crossing - so 5/4x6 boards across joists at 16 inch on-center need 8 screws per 8 ft board.
Explore all our decking calculator tools, or browse the full construction & home improvement diy calculators.
Frequently asked questions
A 10 ft x 12 ft deck (120 sq ft) using 5/4x6 boards (5.5 in actual + 3/16 in gap = 5.69 in module) laid across the 10 ft direction needs 22 rows. With 12 ft boards (one board per row, no joint) that is 22 boards plus 10% waste = 25 boards. Add about 200 deck screws (22 rows x 9 joists x 2 screws ÷ 2 per board crossing).
3/16 inch is the industry standard for wood deck boards - allows the wood to swell when wet without buckling and contract when dry without opening up large gaps. Composite boards expand more with temperature than wood does with moisture; check the manufacturer's spec, often 1/8 inch end-to-end and 3/16 inch side-to-side. Never lay deck boards tight together - they will buckle within one season.
Most decks run boards parallel to the long dimension of the deck (so joists run perpendicular to the long dimension). This means fewer butt joints in each board run. For a 10x12 deck running boards along the 12 ft length, you can use 12 ft boards with no joints in any row - the cleanest look. Boards running across the short dimension hide butt joints better in a rectangular deck but waste more material.
2 screws per joist per board crossing. A 12 ft board crossing joists at 16 inch on-center = 9 joists = 18 screws. For an 8 ft board = 7 joists = 14 screws. Use deck screws (coated or stainless) - never drywall screws, which corrode in the wet outdoor environment. Hidden fastener systems (clips that grip the side of the board) replace topside screws on premium decks.
5/4 boards (one-and-a-quarter) are 1 inch actual thickness - lighter and used for traditional wood deck boards. 2x boards (2x6, 2x8) are 1.5 inches thick and used for joists, beams and heavy-duty deck boards. Many composite decking products are 1 inch thick (5/4 equivalent). Thicker boards span longer between joists - 2x6 can span 24 in joists, 5/4 boards need joists at 16 inch maximum.