Decking Calculator (m² & Linear Metres)

Linear metres are only half the answer

Merchants price decking per linear metre, so converting m² to lm is the usual first step. It isn’t the end: you can’t buy 69.3 metres of decking, you buy whole boards. Every joint has to land on a joist, and a 4.8 m deck with a small overhang won’t come out of a 4.8 m board. This calculator lays out each row and packs the pieces into the lengths you can buy, so you see the number of boards and the real waste.

Typical metric board sizes

• UK softwood: commonly about 120 mm or 144 mm wide, 28–32 mm thick, in 2.4, 3.6 and 4.8 m lengths.
• Australia and NZ hardwood: commonly 86–90 mm or 135–140 mm wide, often sold in random or set lengths.
• Composite: usually about 135–150 mm wide in 3.6, 4.8 or 5.4 m lengths.

Always enter the actual cover width from your supplier’s sheet. Nominal sizes can be several millimetres off.

Structure is local

Joist sizing in the UK, Australia and New Zealand follows national standards and span tables (for example TRADA guidance, AS 1684 and NZS 3604), not the US International Residential Code. This metric tool counts joists at your chosen centres but doesn’t size them. Your timber merchant or local building authority can confirm sizes for your span.