Deck Board Calculator
Enter the deck size, the board length you plan to buy and the joist spacing. The calculator assumes standard 5½ in wide boards (5/4 × 6 or 2 × 6) with a ⅛ in gap, running the length of the deck.
Composite decking usually needs joists at 12 in on center for diagonal layouts and 16 in for straight runs; check the maker’s instructions.
How it’s calculated
- Rows = deck width (in) ÷ (board width + gap), rounded up.
- Linear feet = rows × deck length. Boards = linear feet × (1 + waste %) ÷ board length.
- Joists = deck length (in) ÷ spacing + 1. Screws = 2 per board at every joist.
Materials for common deck sizes
Questions
- How many deck boards do I need for a 12 × 12 deck?
- About 26 rows of 5½ in boards; with 12 ft boards and 10% extra that is 29 boards.
- How many screws per deck board?
- Two at every joist. A 16 ft board on joists 16 in apart takes about 26 screws.
- How far apart should deck joists be?
- 16 in on center is standard. Use 12 in for composite boards laid diagonally or for thinner boards.