I just had a question asked about how much of our Deck Wash would be needed to clean an average 15×15 ft deck. I answered the question on our website www.wash-safe-canada.com in the FAQ section, but I want to remind people who are contemplating cleaning decks not to forget the railings. Believe it or not each lineal foot of railing has 4 sq ft of surface to be cleaned which can really throw off your calculatuons if not included.