Deck Board Spacing Calculator

Calculate total linear feet needed: Area × 12 / (Board Width + Gap). Then divide by board length to get board count. For a 200 sq ft deck with 5.5-inch boards and 1/4-inch gaps: 200 × 12 / 5.75 = 417 linear feet.

For treated wood: 1/8 to 3/16 inch. For composite decking: follow manufacturer specs (typically 3/16 to 1/4 inch). For PVC decking: 1/8 to 3/16 inch. The gap allows drainage and expansion.

10 × 10 = 100 sq ft. Using 5/4x6 boards (5.5 inches actual) with 1/4-inch gaps: 100 × 12 / 5.75 = 209 linear feet. With 12-foot boards: 209 / 12 = 18 boards. Add 10% waste = 20 boards.

Always space deck boards. Tight boards trap water, accelerate rot, and don't allow for expansion. Treated lumber installed wet will shrink, creating natural gaps. Composite and PVC require specific gap sizes per manufacturer.

Linear Feet = (Deck Area × 12) / (Board Width + Gap Width). For a 12x12 deck with 5.5-inch boards and 1/4-inch gaps: (144 × 12) / 5.75 = 300 linear feet. Divide by board length to get quantity.

Yes. Composite decking requires gaps for drainage and thermal expansion. Most manufacturers specify 3/16 to 1/4 inch gaps. Hidden clip systems automatically set the correct spacing. Check your specific brand's installation guide.

Standard overhang is 1 to 1.5 inches past the fascia board. This allows water to drip clear of the substructure. For picture frame borders, the overhang is typically 1/2 to 1 inch.

Start from the house side. Snap a chalk line for the first board. Account for the gap between boards. If the last board would be less than 3 inches wide, adjust spacing or trim the first board. Stagger end joints by at least 12 inches.

A nominal 5/4x6 deck board is actually 1 inch thick and 5.5 inches wide. The 5/4 refers to the rough sawn thickness (1.25 inches), which is reduced to 1 inch after surfacing. Always use actual dimensions for calculations.