How it works
Deck boards are sold by length, and the number you need depends on the deck area, board width, and gap spacing.
Linear feet = Deck area × (1 + Waste%) ÷ Board width (in feet)
Standard board sizes
Common deck boards are 5.5 inches wide (a 6-inch board) or 3.5 inches wide (a 4-inch board). Board length is usually 12, 16, or 20 feet.
Dont forget gaps and waste
Boards are usually spaced with a small gap for drainage. Add about 10 percent for cuts, waste, and mistakes.