The Average Human Body Contains Enough Iron to Make a Nail Over How Many Centimetres Long? Blog Intro: The human body contains enough iron to make a nail over two metres long. In fact, according to the National Health Service (NHS), the average person has about 3.7g of iron in their body — more than enough to make a standard-sized nail. So, what is iron used for in our bodies? The NHS lists that it is "a vital part of haemoglobin, which carries oxygen around the body".