How to calculate deck
Rows = Deck width ÷ (board width + gap); Boards = rows × (1 + waste)
Worked example. Boards needed: 29 × 16 ft boards.
Example inputs — Deck length: 16 ft; Deck width: 12 ft; Board width: 5.5 in (standard 6"); Gap between boards: 0.13 in; Waste allowance: 10%. Starting values are illustrative.
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
Boards run along the deck's length, so we divide the width by board spacing (width + gap) to get rows, then add your waste allowance for cuts and defects.
Assumptions & limitations
- Boards run the full length of the deck
- Screw estimate assumes joists 16" on center, 2 screws per joist crossing
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
What about joists and posts?
This covers surface boards. Joists are typically 16" on center — a separate framing plan is recommended.