How the deck board calculator works
It works out how many rows of boards fit across the deck (each row is one board width plus the gap), then how many boards each row needs at your chosen length. Screws are counted at two per board at every joist it crosses.
The formula
rows = deck depth ÷ (board width + gap), rounded up
boards per row = deck length ÷ board length, rounded up
boards = rows × boards per row × (1 + waste %)
screws = rows × joists × 2
Tips
- Pick a board length that matches your deck. On a 16 ft deck, 16 ft boards mean no joints and almost no waste. With 12 ft boards you’d need two per row and throw away 8 ft from each pair, unless you plan the offcuts carefully.
- Actual vs. nominal width: a “2×6” or “5/4×6” board is really 5½ in (14 cm) wide. Composite boards vary, so check the spec sheet.
- Gap: most wood decking uses about 3/16 in (5 mm). Composite manufacturers specify their own gap, often with hidden fasteners instead of face screws.
- Hidden fasteners replace face screws on many composite boards. Count clips from the manufacturer’s coverage chart instead.