The puddled iron (wrought iron) structure of the Eiffel Tower weighs 7,300 tonnes, while the entire structure, including non-metal components, is approximately 10,000 tonnes. As a demonstration of the economy of design, if the 7,300 tonnes of the metal structure were melted down it would fill the 125-metre-square base to a depth of only 6.25 cm (2.5 in), assuming the density of the metal to be 7.8 tonnes per cubic metre.[50] Additionally, a cubic box surrounding the tower (324m x 125m x 125m) would contain 6,200 tonnes of air, almost as much as the iron itself. Depending on the ambient temperature, the top of the tower may shift away from the sun by up to 18 cm (7.1 in) because of thermal expansion of the metal on the side facing the sun.[51]