Deck Boards Calculator
Ordering the right quantity of decking is essential to avoid running short mid-project or buying more than you need. This deck boards calculator takes the deck length and width in feet, the board width in inches (the actual measured width, not the nominal size), the gap between boards in inches, and a waste factor. It calculates the number of rows of decking across the deck width, the total linear feet required, and the number of boards at a given length. The default board width is 5.5 inches, which is the actual width of a standard nominal 2x6 or 5/4x6 deck board. The default gap is 0.25 inches (1/4 inch), which provides good drainage while still looking tight. Composite and PVC decking manufacturers specify their own required gaps, typically 3/16 inch end-to-end and 3/16 inch side-to-side; check your product's installation guide. A 10% waste factor covers end cuts, boards with defects, and board selection waste. For diagonal decking patterns, use 15 to 20% waste. The calculator shows results at the standard board lengths of 8, 12, 16, and 20 feet so you can choose the length that minimises waste for your specific deck dimensions. For a deck that is exactly 16 feet long, 16-foot boards eliminate end joints entirely.
Deck boards formula
Rows = ceil(Deck width (in) / (Board width + Gap))
Linear feet = Rows x Deck length
Linear feet with waste = Linear feet x (1 + Waste% / 100)
Boards = ceil(Linear feet with waste / Board length)
Worked example: 20 x 12 ft deck, 5.5 in boards, 0.25 in gap, 10% waste, 16 ft boards
- Deck width in inches: 12 x 12 = 144 in
- Rows: ceil(144 / (5.5 + 0.25)) = ceil(25.04) = 26 rows
- Linear feet: 26 x 20 = 520 ft
- With 10% waste: 520 x 1.10 = 572 ft
- Boards at 16 ft: ceil(572 / 16) = 36 boards
Deck boards calculator: frequently asked questions
How do I calculate deck boards needed?
Divide the deck width by the board width plus the gap between boards to find the number of rows. Multiply by the deck length to get total linear feet. Add your waste factor (10% is standard) and then divide by the board length to find how many boards to buy. This calculator automates those steps.
What gap should I leave between deck boards?
A gap of 1/8 to 1/4 inch between deck boards allows for drainage, debris clearance, and seasonal wood movement. Pressure-treated lumber expands and contracts with moisture changes. Many installers butt boards tight when green (freshly treated), knowing they will dry and gap naturally. For composite or PVC decking, follow the manufacturer's installation guide for required spacing, which is often 3/16 inch.
What is the actual width of a 2x6 deck board?
A nominal 2x6 board is actually 1.5 inches thick and 5.5 inches wide. A nominal 5/4x6 deck board is actually 1 inch thick and 5.5 inches wide. The 5/4x6 (pronounced five-quarter) is the most common deck board size in the US. This calculator defaults to 5.5 inches (5/4x6 actual width). Always use actual dimensions, not nominal, when calculating coverage.
How long should my deck boards be?
Deck boards typically run the full length of the deck or span between joists. Common lengths are 8, 12, 16, and 20 feet. Longer boards mean fewer end joints and a cleaner look but are heavier and harder to handle. For decks longer than 20 feet, boards will need to be spliced; stagger the joints so they do not line up in the same joist bay. Always end-cut and seal treated lumber cuts with an end-cut solution.
Do I need to acclimate deck boards before installation?
Pressure-treated lumber is wet when it leaves the treating plant. Stack it with spacers (stickers) for several weeks before installation to allow it to dry partially. If you install it while soaking wet, gaps will be excessive once it dries. For composite and PVC decking, acclimation is not typically required but always check the manufacturer's installation guide.
Sources
- American Wood Council DCA6 prescriptive residential wood deck construction guide: awc.org.
- Southern Pine Council deck design guide: southernpine.com.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. Check local building codes and obtain permits before construction.