According to this source... http://www.madsci.org/posts/archives/2001-02/981770369.An.r.html" [Broken] ...there's 28.8 kg of hard tissue per 70 kg adult human, made up of ~4 trillion cells. There's 31 trillion blood and related non-tissue cells, thus a grand total of 35 trillion human cells, and there's ~40 trillion bacteria in the colon. Thus the average tissue cell masses ~7.2E-12 kg and so contains ~688 trillion atoms at an average atomic mass of 6.3. If you exclude the 10% hydrogen, the average atomic mass is 15, so there's ~260 trillion non-hydrogen atoms per cell. There seems to be a lot of non-cellular material in the body, mostly water in all likelihood.