text: The answers about 1kg being 1kg no matter what the metal are correct.\n\nThe heaviest metal is Osmium which has a specifc gravity of approx 22 and a half - meaning that it weights 22 and a half times as much as water, to put it into context a bucket of water weighs about 10kg but a bucket of osmium would weigh nearly quarter of a ton.  It's about twice as heavy as lead.\n\nJust out of interest, if you had a lump of anti-matter about the size of a marble it would weight the same as the whole earth.