I read there is as many Bitcoin addresses as the sands on the earth. Although the chances to generate the same Bitcoin address is small... everyone should take precaution by spreading their coins in multiple addresses.
There is a video on youtube, from the Bitcoin network that use this
as a example, but they say that the sand on the earth and a few thousand other planets will not be enough to equal the math needed to calculate the Addresses that can be created from that algorithm.
I haven't seen that video, but you are right that the number of grains of sand on Earth is nowhere close to the number of bitcoin addresses.
According to
http://www.quickanddirtytips.com/education/math/how-many-grains-of-sand-are-on-earth%E2%80%99s-beaches, there are 5.6x10^21 grains of sand on Earth.
According to
https://www.quora.com/Are-there-more-stars-than-grains-of-sand, there are 10^24 grains of sand on Earth.
According to
http://www.npr.org/sections/krulwich/2012/09/17/161096233/which-is-greater-the-number-of-sand-grains-on-earth-or-stars-in-the-sky, there are 7.5 x 10^18 grains of sand.
No idea which of these estimates are accurate, but let's take the largest one, ie 10^24.
On the other hand, there are 2^160 or 1.46x10^48 bitcoin addresses, which is 1,460,000,000,000,000,000,000,000 times larger the the number of grains of sand.
