Deck size, board width and joist spacing in. Lineal metres with waste, board count in 5.4m lengths, joists and the screw box out. Free, no email.
90mm (hardwood standard), with a fixed 5mm gap between boards for drainage and timber movement.
450mm (standard). Tighten to 400mm for 140mm boards or diagonal laying.
284 lineal metres
43 rows of 90mm boards over a 6m x 4m deck (24.0 m²)
Includes a 10% docking and waste allowance for offcuts, checked ends and joins landing on joists. In 5.4m stock lengths that is about 53 boards.
15 joists, 60 lineal metres
Running across the 4m width at 450mm centres along the 6m length, end joists included. Bearers, posts and footings are on top of this.
~1,300 screws
1,290 exactly at 2 per board per joist, rounded up to the nearest 100. Buy the 500 box (or the bucket), snapped heads and dropped screws are a certainty.
Guide only. Joist size, bearer spans, stirrup heights and fixing types come from the span tables and the frame design for your timber and site, not this page. Decks over 1m high and structural work need the right approvals, check with your council or building surveyor.
A client says 6 by 4. The yard wants lineal metres of 90mm merbau, the screw aisle wants a box count, and you want to know it before you quote, not after the second delivery fee. Rows times length plus 10% for docking gets you there, this just does the arithmetic while you are still on the phone.
Switch between 86mm, 90mm and 140mm boards and watch the rows and screw count move. The joist figure covers the deck frame layer at your spacing, so the one screen gives you boards, joists and fixings for the supply run and a sanity check on any quote.
Divide the deck width by the board width plus the 5mm gap to get the number of rows, then multiply rows by the deck length. A 4m wide deck in 90mm boards is 4000 ÷ 95 = 43 rows, and at 6m long that is 258 lineal metres before waste. Add 10% for docking and offcuts and you land around 284.
Docking. Every board gets its ends trimmed square, joins have to land on a joist, and merbau packs usually include a few boards with checked or split ends you will cut around. Ten percent is the standard allowance, and running short on decking mid-job usually means a colour mismatch on the top-up pack.
450mm centres is the common standard for 86mm and 90mm hardwood boards laid square. Drop to 400mm for 140mm wide boards or any diagonal laying, because the effective span between supports grows. Softwood boards and some composites need tighter spacing again, so check the manufacturer's span chart.
Only partly. It counts the joists running across your deck and their lineal metres, but joist size, bearer spans, post spacing and footing depth come from the span tables for your timber grade and your soil, not from a calculator. Decks over 1m high need engineering and approvals in most states, so talk to your council or building surveyor before you dig.
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