The common claim that there are ~7.5E18 (~2.5 × 2⁶⁴) grains of sand seems to originate from this back-of-the-envelope calculation: https://web.archive.org/web/

The common claim that there are ~7.5E18 (~2.5 × 2⁶⁴) grains of sand seems to originate from this back-of-the-envelope calculation: https://web.archive.org/web/19990117001023/http://www2.hawaii.edu/suremath/jsand.html https://web.archive.org/web/19990117001023/http://www2.hawai... It takes only beach sand into account, and of course there's a lot of guessing involved. It could be easily off by many orders of magnitude.