Deck Board Spacing Calculator
Enter a fixed width, a board count, and board width to get the exact gap size — with or without equal gaps at the edges.
Gap between boards
0.5556 in
- Mode
- Gaps between boards only
- Remaining space
- 5 in
- Number of gaps
- 9
›Calculation details
remaining space = total width − (number of boards × board width)
gap = remaining space ÷ (number of boards − 1)
How it works
Remaining space is your total width minus the space every board itself takes up. That leftover space then gets divided evenly across the gaps — either just the gaps between boards, or every gap including the two at the outer edges, depending on which mode you pick. The two modes give different gap counts for the same layout, so the result changes noticeably between them.
FAQ
Which mode should I use?
“Gaps between boards only” fits boards flush to a frame or border. “Equal edge + internal gaps” centers the whole layout with a matching margin on both sides — more common when there's no frame to butt against.
What if it says the boards don't fit?
Your board count × board width already exceeds the total width, leaving no room for any gap at all — reduce the board count, use narrower boards, or work with a wider total width.