Deck Board Calculator
Calculating deck boards requires knowing the deck dimensions, the actual (not nominal) board width, the gap between boards, and the board pattern. A standard 2x6 deck board has an actual face width of 5.5 inches, not 6 inches. A 2x4 is 3.5 inches wide. Enter the actual dimensions to get accurate results. The calculator determines how many runs of boards span the deck width, then converts the total linear footage needed into board counts at common lumber lengths of 8, 10, 12, and 16 feet. A diagonal (45-degree) pattern requires approximately 41 percent more linear footage than a straight pattern, because boards cross the deck at an angle. Always add a waste factor: 10 percent for straight patterns, 15 percent or more for diagonal or herringbone patterns. The gap between boards is typically 0.25 inches for pressure-treated wood (which shrinks as it dries) and 0.125 to 0.1875 inches for composite decking. Check your product's installation manual for the specified gap.
Deck board formula
Runs = Ceiling(Deck width (in) / (Board width (in) + Gap (in)))
Linear feet = Runs x Deck length x Diagonal factor
Diagonal factor = 1.0 (straight) or 1.414 (45 degrees)
Total with waste = Linear feet x (1 + Waste %)
Boards at N ft = Ceiling(Total LF / N)
Worked example (straight pattern)
Deck: 16 ft x 12 ft. Board: 5.5 in wide, 0.25 in gap. Waste: 10%.
- Deck width in inches = 12 x 12 = 144 in
- Runs = Ceiling(144 / 5.75) = 26 runs
- Linear feet = 26 x 16 = 416 LF
- With 10% waste = 416 x 1.10 = 457.60 LF
- Boards at 16 ft = Ceiling(457.60 / 16) = 29 boards
Frequently asked questions
How many boards do I need for a deck?
Divide the deck width (perpendicular to the boards) by the effective board coverage (board width plus gap). This gives the number of board runs. Multiply by the deck length to get total linear footage, then divide by board length to get the board count. Add 10 percent for waste.
What is the standard gap between deck boards?
A gap of 1/4 inch (0.25 in) is standard for pressure-treated lumber, which will shrink as it dries. Composite decking manufacturers typically specify gaps of 1/8 to 3/16 inch; check your product's installation guide. The gap allows water drainage and air circulation.
What is the actual width of a 2x6 deck board?
A nominal 2x6 deck board has an actual face width of 5.5 inches. A nominal 2x4 has an actual width of 3.5 inches. Always use actual dimensions, not nominal, when calculating board counts.
Does a 45-degree diagonal pattern require more boards?
Yes. A diagonal (45-degree) pattern increases the linear footage of boards required by approximately 41 percent compared to a straight pattern (a factor of about 1.414). This calculator accounts for the diagonal factor in the board count.
Should I add a waste factor for deck boards?
Yes. Add at least 10 percent for straight patterns and 15 percent for diagonal patterns to account for end cuts, defects, and measurement errors. Some contractors add up to 15 to 20 percent for complex deck shapes.
Sources
- American Wood Council: Prescriptive Residential Wood Deck Construction Guide (DCA6).
- US Forest Products Laboratory: wood shrinkage and drying data.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. Confirm actual board dimensions with your lumber supplier before ordering.