Calculators/ Framing & Exterior/Deck Board Calculator
Deck Board Calculator
Deck boards, joists and fasteners for a deck.
Decking coverage depends on the gap as much as the board. A quarter inch gap instead of an eighth adds a whole extra row across a typical deck, so decide the gap before you buy rather than after.
How this is calculated
- Each row covers the board width plus one gap. A 5½ inch board with an eighth inch gap covers 5.625 inches, or 0.469 feet.
- Rows = deck width ÷ coverage per row, rounded up.
- Total linear feet = rows × the length each board runs. Divide by the stock length you can buy to get board count.
- Joists at the chosen spacing across the board run, plus one for the closing joist. Composite decking usually requires 16 inch spacing or tighter.
Frequently asked questions
What gap should I leave between deck boards?
An eighth of an inch for kiln-dried or composite boards, which barely shrink. Wet pressure-treated lumber can be butted tight, because it will shrink to leave its own gap as it dries.
What joist spacing does decking need?
Sixteen inches on centre suits most wood decking. Composite boards often require 16 inches for perpendicular installs and 12 inches for diagonal.
How many screws per deck board?
Two at every joist crossing. That is the figure used here, and it works out at roughly 350 screws per 100 square feet of deck.