Decking Calculator
Calculate decking materials from area and board size.
Boards to buy
47
21 rows × 2 boards per row
Deck area
12 m²
Exact boards
42
Rows
21
In-depth explanation
Estimate how many deck boards you need from deck size, board size, and gap between boards, with wastage. Everything runs locally in your browser — your inputs are not uploaded to produce the result.
Boards need spacing for drainage and expansion — often a few millimetres. This counts surface boards only. Frame materials are separate.
Around 10% is a sensible starting point for cuts and defects. Tweak the inputs above to compare options, then copy or note the result you need.
Board width plus gap determines how many boards cover the width. Gaps are for drainage and expansion — too tight and the deck cups. This counts the walking surface, not joists, posts, or screws.
Wastage covers mitres and bad boards. Hidden-fix systems can change spacing. Check span tables for the timber you use; this is a materials count, not an engineering design.
Frequently asked questions
Why include a gap?
Boards need spacing for drainage and expansion — often a few millimetres.
Does this include joists?
No — this counts surface boards only. Frame materials are separate.
What wastage should I use?
Around 10% is a sensible starting point for cuts and defects.
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