Deck Board Calculator

How It Works

This calculator determines how many deck boards you need by dividing your deck width by the board width (plus gap) to get rows, then figuring out how many boards end-to-end cover the length. A 10% waste factor covers angled cuts and defective boards.

The Formula

Variables

• DeckWidth_in — Deck width in inches (perpendicular to board direction)
• BoardWidth — Actual board width in inches (5.5" for a 2x6)
• Gap — Spacing between boards for drainage (typically 1/8")
• DeckLength — Deck length in feet (direction boards run)
• BoardLength — Length of each board in feet (8, 10, 12, or 16)

Example

A 16 ft x 12 ft deck with 5.5" boards (12 ft long), 1/8" gap: 144 in / 5.625 in = 26 rows, 16/12 = 2 boards per run, 52 boards. With 10% waste = 58 boards. At $12 each, board cost is $696.

Tips

• Composite decking costs more upfront ($20-40/board) but requires zero maintenance and lasts 25+ years.
• Run boards perpendicular to the house for the best appearance and to minimize visible end joints.
• Pre-drill screw holes to prevent splitting, especially at board ends.
• Leave a 1/8" gap between boards and a 1/4" gap at the house wall for expansion.
• Most municipalities require a building permit for decks over 30 inches above grade.