Question: How many atoms does a human body have?

Edward Guy answered on 8 Mar 2023: last edited 8 Mar 2023 12:52 pm

Great question… let’s have some fun calculating this (scientists love this kind of stuff!). First, we need to know how heavy atoms are, and then see how many of those atoms weigh the same as a person. We are made mostly of water; H2O (mass of 18 because H is 1 and O is 16) and Carbon (12)… plus smaller amounts of sulphur, nitrogen, phosphorous and lots of trace elements). But we can assume we are mostly water (which has a molecular mass of 18 average and therefore the atomic mass of each of the 3 atoms in H2O is 18/3 = 6). We can get from atomic mass to grams because we know 6.023 x 10^23 atoms (Avogadro’s number) of any element weigh the same in grams as the atomic mas of the element. So, that many oxygen atoms (atomic mass 16) weigh 16 grams, and so on. We calculated anaverage atomic mass of 6, so 6g of us contains 6 x 10^23 atoms. If we weigh 60kg, we just multiply 6g x 10,000, so a 60kg person has 6 x 10^27 atoms! That’s 6,000,000,000,000,000,000,000,000,000 or 6 billion billion billion atoms. Now, THAT’S science!