I don't think I fancy the comparison used. Bitcoins and sand, sounds like negative connotation...
Well, I had already done the comparaison with gold earlier in this thread, so I wanted to change.
But I should have sticked with gold. That's what bitcoin is : electronic gold. And it's actually even better, since gold is not very easy to handle in very small quantities.
Anyway, here is the comparaison with gold.
In the whole world, there are about 150,000 tons of gold. That's 150 billions of kilograms, and about 5 billions of onces. All those numbers represents the same quantity.