13 jun 2012 , work out how many square metres the area is, this is done by length x width e.g. 6 x 4 = 24m²; to cover 1m² with ecodek® composite decking you need 7.1 , therefore to work out how many screws you will need calculate m² x 40 e.g. 24 x 40 = 960; ecodek sell screws in multiples of 200s therefore 1000,