5.1m Deck boards 5.1m deck board, Tanalised green redwood- ex. 32mm x 125mm (5") , grooved one side, smooth reverse £17.85 Out of stock. 0 in your basket View Basket Checkout Please use the drop down menu for the quantity of deck boards you require. Note; each deck board is 125mm wide x 28mm thick and 5.1m long. There is 8.33m of decking required to cover one square meter. To work out how many 5.1m deck boards you need to cover the area you have follow the method below; If you have 60 square metres needed multiply 60 by 8.33 which gives 499.8 linear metres of decking needed, Then divide the metres of decking needed by the 5.1m deck board length to give the number of deck boards needed, So, 499.8 divided by 5.1 gives 98x 5.1m deck boards needed.