DCK

Decking Calculator

The deck boards and joists for a rectangular deck, with a waste allowance.

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Result…

Units
m
m
mm
mm

3–6 mm (⅛–¼ in) for drainage.

m
mm

Centre to centre; 400 mm or 16 in is common.

%

For cuts and breakage; 10% is usual, 15% for diagonal layouts.

 

…

How it's calculated

Rows = deck width ÷ (board width + gap), rounded up
Boards = rows × deck length × (1 + waste %) ÷ board length, rounded up
Joists = deck length ÷ spacing, rounded up, + 1

Counts the deck boards for a rectangular deck from the board width, the gap and the length you buy them in, with a waste allowance for cuts and end joins. It also counts the joists under the boards at your spacing. Board ends should land on a joist, so choose a board length that suits the spacing.

Your numbers, step by step

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