999.5 Gold bars are 1 kilogram (31.990 fine troy ounces) gold cast bar, of minimum fineness 995.0, and bearing a serial number and identifying stamp. To quantify this there are two major systems that measure purity. They are carat (karat in the US), and fineness. Both carat and fineness give figures that indicate the proportion of pure gold to other base metals in gold jewellery and products.