Deck Board Gap Calculator: Spacing, Coverage & Fit
Check the arithmetic behind a board layout: total open gap, covered width, maximum boards that fit and the difference between the planned layout and the available width.
Board gap inputs
Deck board spacing result
The board-gap formula
Board coverage = board count × board width
Occupied run = board coverage + total internal gap + edge clearances
Why one gap calculation is not enough
A deck can have the correct number of boards and still fail to fit because board width and gap are both physical dimensions. Checking the complete occupied run reveals whether the chosen layout exceeds or leaves space within the available width.
Worked example
28 boards with a 140 mm face width and 6 mm gaps have 3.92 m of board face plus 27 × 0.006 m of internal gap, for 4.082 m before any edge clearance.
Edge conditions
This calculator keeps start and end clearances separate. That makes it easier to distinguish the gaps between boards from perimeter spacing, which may be governed by the installation system.
Frequently Asked Questions
Does the formula count the gap before the first board?
No. Only the internal gaps between adjacent boards are counted.
Can the calculator find the maximum board count?
Yes.
Should I use nominal board width?
Use the actual coverage width of the installed product.
Does this recommend a deck-board gap?
No.