Decking timber is sold by the linear metre (LM), the total length of board you buy, while decks are usually planned in square metres (m²) of area. Converting between the two is the most common step people get wrong.
The short version: divide your deck area by the board's cover width (board width plus the gap between boards, in metres) to get linear metres, then add a wastage allowance for cuts and offcuts. Our timber calculator does this for you and shows the working.