Deck Board Calculator: Boards, Rows, Gaps & Waste
Estimate deck-board rows and purchasable boards using the actual face width, selected installation gap and stock length. See the effect of waste instead of burying it inside one unexplained quantity.
Deck dimensions
Decking quantity result
How deck board quantity is calculated
The board face width and installation gap jointly determine how many rows are needed across the deck. The number of stock pieces per row then depends on the board direction and available board length.
Rows = ceiling((deck width + gap) ÷ row coverage)
Boards per row = ceiling(board run ÷ stock board length)
Base boards = rows × boards per row
Planning boards = ceiling(base boards × (1 + waste))
Worked example
A 6 × 4 m deck with a 140 mm board face and 6 mm gap needs approximately 28 rows across 4 m. If 4.8 m stock boards run along the 6 m direction, two stock pieces per row are needed, creating a 56-board base requirement before waste.
Why actual face width matters
A nominal board width can differ from the installed face width. Entering the wrong width can move the row count across a threshold and change the entire material requirement.
Where simple calculations stop
Complex perimeter borders, short pieces around posts, angled boards, breaker boards and unusual deck shapes can create significantly different cutting patterns. Treat this as a rectangular-layout estimate.
Frequently Asked Questions
Does the gap count toward deck width?
Yes.
Does waste automatically create extra full boards?
Yes. The planning quantity is rounded upward to whole boards.
What happens when the board is shorter than the run?
The calculator increases boards per row so the run can be covered with stock pieces.
Can I use feet instead of metres?
Yes.