It's not that big a feat to count all the sand in the universe. Mathematicians have been doing it for centuries. Given, their findings are based on many assumptions. Such as the definition of sand grains. Are they small pebbles, microscopic shells, minerals, etc. All these things have mass, so you can create estimates of how much the universe contains. The older, much older, Muslim mathematicians even did this. Back when science was still a thing in Islam.