# Just a drop in the bucket

If approximately $$70 \%$$ of the Earth's surface is covered with water, what is the order of magnitude for the number of raindrops in the world's oceans?

Hint: The order of magnitude of $$2478 = 2.478 \times 10^{3}$$ is $$3$$.

Details and assumptions

• The earth's radius is $$6380~\mbox{km}$$.
• The radius of a raindrop is $$1~\mbox{mm}$$; raindrops can be approximated to be spherical.
• The average ocean depth is $$2~\mbox{km}$$.
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