Decking Calculator

Estimate how many decking boards you need from the deck size, board width, board spacing and board length. See the deck area, the total board length required and the board count.

Enter the deck size in metres, the board width and the gap between boards in millimetres, plus the length of a single board. The calculator finds the deck area, the total length of board needed (accounting for the gaps) and how many boards that is.

Deck area
Total board length
Boards required

A decking calculator works out how much decking timber to buy from the deck area, accounting for the width of each board and the gap left between them, then converts that into a number of boards.

The maths

  • Deck area = length × width
  • Coverage per metre = (board width + gap) ÷ 1000 m² per metre run
  • Total board length = deck area ÷ coverage per metre
  • Boards = total length ÷ single board length, rounded up

Examples

  • 4 m × 3 m deck with 140 mm boards and 5 mm gaps = ~9.9 m²
  • That needs about 68 m of board run
  • With 4 m boards, order 17 boards

Frequently asked questions

Does this allow for waste?

Not explicitly. Add 5–10% to the board count for off-cuts and mistakes, especially on irregular shapes.

What about the subframe and fixings?

This estimates boards only. Joists, posts, screws and flashing need to be priced separately based on your frame design.

Just for the giggles, much love.
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