Materials
Deck board rows & equal gaps
- where
- clear span (mm)
- overall width (mm)
- edge gap each side (mm)
- full-width boards
- maximum gap (mm)
- board width (mm)
- actual gap (mm)
Explain this equation
Finds the fewest full-width deck boards that fill a width without any gap exceeding your maximum, and then the equal gap between them.
W is the overall width, e the gap left at each edge, and s the clear span between those edge gaps. b is the board width and gmax the largest gap allowed. n is the number of boards, and g the actual equal gap. All are in millimetres.
n boards have n − 1 gaps between them, so the span is nb + (n − 1)g. Setting g to gmax and solving for n gives the expression in the ⌈ ⌉ brackets. Rounding up means the boards fit with a gap no bigger than gmax. Sharing the leftover space equally across n − 1 gaps gives g.
A 3000 mm width with 5 mm edges, 140 mm boards and 6 mm maximum gap needs 21 boards at 2.5 mm gaps.
Watch out: if full boards cannot fit with a positive gap, the calculator stops. You will then need to rip a board. Use the supplier's moisture-related gap.
Find the minimum board count with gaps not exceeding the chosen maximum.
Enter your values to see the result.
Good to know
All boards assumed full width. Rejects a negative gap: rip an edge board or revise the layout. Use the supplier’s moisture-dependent gap and fixing details.
Limits
Flooring gaps, slide clearances, fire-door gaps, fixing schedules and finishes must follow the design and product instructions.
Sources
- Geometry / arithmetic
This is a calculation aid, not a structural design or compliance certificate. Every default is an example, not a specification for your project.