# Grains of Sand

Have you ever sat on a beach and wondered how many grains of sand there
were? I have, but I may be a special case. Today we’re going to take
that a step further, and figure out how many grains of sand there are on
the entire earth. (Caveat: I’m only going to consider sand above the
water level, since I don’t have any idea what the composition of the
ocean floor is). I’m going to start by figuring out how much beach there
is in the world. If you look at a map of the world, there are four main
coasts that run, essentially, a half circumference of the world. We’ll
say the total length of coast the world has is roughly two
circumferences. As an order of magnitude, I would say that the average
beach width is 100 m, and the average depth is 10 m. This gives a total
beach volume of

“The total number of stars in the Universe is larger than all the grains of sand on all the beaches of the planet Earth”

If we just use our beach volume, that gives a total number of grains of sand as \~1*10^20, which is large, but not as large as what we found above. Is that less than the number of stars in in the universe? Well, that’s a question for another day (or google), but the answer is, to our best estimate/count, yes.

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