Deck Board Calculator
Deck boards, joists and fasteners, with the installation gap that differs between wet treated lumber and pre-dried or composite boards.
Deck Board Calculator
Board count, fasteners and the gap. Wet treated lumber shrinks as it dries and kiln-dried does not, so the right gap at installation is different for each — and getting it backwards shows.
| Deck area | — |
|---|---|
| Coverage per board | — |
| Rows of decking | — |
| Boards (with waste) | — |
| Linear feet | — |
| Joists | — |
| Fasteners (approx) | — |
Rows are deck width ÷ (board width + gap), rounded up. Fasteners assume two per
board per joist crossing, which is the ordinary pattern for face-screwed decking; hidden fastener
systems have their own counts.
The gap is the part that goes wrong. Pressure-treated lumber is usually delivered wet and shrinks
across its width as it dries, so it is normally installed butted tight and opens up on its own. Kiln-dried
wood and composite are already at or near their final width, so the gap has to be built in at
installation or the deck will not drain. Follow the manufacturer's instruction for the specific board
— composite in particular has required gaps that also change with the temperature on the day.