Deck Board Calculator

How to Calculate Deck Boards Needed?

The number of deck boards depends on the deck width, the board width, and the gap between boards. Divide the deck width (in inches) by the sum of one board width plus one gap. This gives the number of boards needed across the deck. Each board is cut to the deck length. A 12-foot wide deck using standard 5.5-inch boards (2x6) with 1/8-inch gaps: 144 inches / 5.625 inches = 25.6, rounded up to 26 boards, each 16 feet long if the deck is 16 feet. The calculator above handles this math and adds your chosen waste percentage.

What Size Deck Boards Should I Use?

The most popular deck board is the 2x6 (actual width: 5.5 inches). It provides a good balance of surface coverage per board and structural rigidity between joists. 2x4 boards (3.5 inches actual) are occasionally used for narrow-profile designs but require closer joist spacing because they are more flexible underfoot. 5/4x6 radius-edge decking (actual 1 inch thick, 5.5 inches wide) is lighter, has rounded edges for bare-foot comfort, and is the standard profile for both pressure-treated and composite decking. Composite boards come in 5.5-inch and 7.25-inch widths, with wider boards covering more area per piece and reducing the number of fastener rows.

What Gap Should I Leave Between Deck Boards?

A 1/8-inch gap is standard for pressure-treated lumber installed at its as-delivered moisture content (which is high). As the wood dries over the first season, the gap widens to approximately 3/16-1/4 inch. For kiln-dried or composite boards that have already reached their stable dimension, install with a 3/16-inch gap. The gap allows water to drain through the deck surface, reducing standing moisture that causes rot and mold. It also allows for minor seasonal expansion. Some hidden fastener systems set the gap automatically to a consistent 3/16 inch. For grooved-edge composite boards, the clip-and-fastener system defines the exact spacing.

How to Calculate Total Linear Feet of Decking?

Multiply the number of boards by the board length. If you need 26 boards, each 16 feet long, the total linear footage is 416 feet. Lumber yards sell deck boards in even lengths (8, 10, 12, 14, 16, and sometimes 20 feet). If your deck is 14 feet long, you would buy 14 or 16-foot boards. Buying 16-foot boards for a 14-foot deck creates 2-foot offcuts per board, which can sometimes serve for short sections, stair treads, or bench slats. Planning cut layouts in advance reduces waste and total cost.

How Many Deck Screws Do I Need?

Standard face-screwing uses two screws per board at every joist crossing. With joists at 16 inches on center, a 16-foot board crosses approximately 12 joists, requiring 24 screws. For 26 boards, that totals roughly 624 screws. A 5-pound box of deck screws contains about 350 screws (for #8 x 2.5-inch or 3-inch screws), so two boxes cover this project. Hidden fastener systems use one clip per board per joist, reducing the visible hardware to zero but adding clip cost. Stainless steel or coated screws are mandatory for treated lumber and composite decking to prevent corrosion staining.

Pressure-Treated vs Composite vs Cedar Deck Boards

Pressure-treated pine is the most affordable decking at $1.50-$3.00 per linear foot. It requires staining or sealing every 1-2 years and lasts 15-25 years with maintenance. Cedar costs $3.00-$5.00 per linear foot, resists rot naturally, and weathers to a silver-gray if left untreated. Composite decking (Trex, TimberTech, Fiberon) runs $4.00-$10.00 per linear foot but requires almost no maintenance and lasts 25-50 years. PVC decking is $6.00-$12.00 per linear foot, completely synthetic, and will not absorb moisture. The higher upfront cost of composite and PVC pays off in reduced lifetime maintenance expense for homeowners who want a low-effort outdoor space.

How Much Waste Should I Plan For?

A 5% waste factor works for rectangular decks where board lengths match available lumber lengths. A 10% factor suits decks with angled cuts, picture-frame borders, or board lengths that do not match standard lumber sizes. A 15% factor is appropriate for complex multi-level decks, curved edges, and diagonal board patterns that require angled cuts on every board. Diagonal decking increases waste because each board end is cut at 45 degrees, and the starting and ending boards are progressively shorter triangles that cannot be reused elsewhere.

Board Layout Tips for a Professional Finish

Stagger end joints randomly so no two adjacent boards end on the same joist. Each butt joint should sit centered on a joist with both board ends fastened. Sight down each board before fastening and orient the crown (slight arc from end to end) facing up so the board does not hold standing water. For pressure-treated lumber, place the bark side up (the side that was facing the outside of the tree) because it sheds water more effectively and cups less as it dries. Start the layout from the house side and work outward so the last board (which may need ripping to width) is at the far edge where it is least visible.

Frequently asked questions