: I've reviewed my math. Slow down and check your own math - find a reference giving iron in density per cubic meter, they aren't very common. Much more common is gram per cubic centimeter. See Iron - density of 7.8 g/cm^3. Conversion of cubic centimeter to cubic meter is a factor of a million (100^3 gives 1e6). 7.8 million grams is 7800 kilograms is 7.8 tons.