Estimate board rows, lengths and purchasing quantities from a rectangular deck layout.
Method and practical checks
Rows = ceiling of (deck width + gap) divided by (board width + gap). Boards per row round up from stock length.
This conservative count does not optimize offcut reuse, allow for structural spans or design the subframe. Follow the board manufacturer’s gap and support guidance.
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How the Decking Board Calculator works
Boards run along the deck length; rotate the dimensions to change orientation.
Rows = ceiling of (deck width + gap) divided by (board width + gap). Boards per row round up from stock length.
This conservative count does not optimize offcut reuse, allow for structural spans or design the subframe. Follow the board manufacturer’s gap and support guidance.
Worked example
A deck 4 m wide with 140 mm boards and 5 mm gaps needs (4,000 + 5) ÷ 145 = 27.6, so 28 rows. Each 5 m row needs 2 boards of 3 m, giving 56 boards, or 62 with a 10% allowance (186 m of board).
Pre-filled values
Input
Value
Length
5 m
Width
4 m
Board width
140 mm
Board gap
5 mm
Stock board length
3 m
Extra allowance
10 %
Calculated result
Result
Value
Board rows
28
Boards per row
2
Boards before allowance
56
Boards to buy
62
Purchased board length
186 m
Reading the result
This is a conservative count: offcuts are not reused, so experienced installers may need fewer boards.
Follow the board manufacturer’s gap and joist spacing; they affect drainage and structural span.
Joists, screws and fascia boards are separate items.
