I read that there are more stars in the Universe, than all the sand granules of the Beach. Is this true? How?

I want technical replies. Even a fistful of sand will have atleast 100000 visible particles, excluding dust. If that is so, how can we have more stars than sand. I want astro-physics students to reply with proof. First do we have any count of the number of sand granules we have ? If not how did some scientist come out with this fact? Mathmatical answers with calculable proof would be great.