The classic internet addressing system, IPv4, uses 32-bit addresses. How many different addresses does that allow?
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Answer
About 4.3 billion addresses
The central pool of free addresses ran dry in 2011, and blocks of them are now bought and sold for tens of dollars per address.
How to estimate it
Each bit doubles the number of possible addresses, so the answer is 2 multiplied by itself 32 times. A handy shortcut: 2^10 is 1,024, about a thousand. So 2^30 is about a billion, and 2^32 is 4 times that: roughly 4 billion. The exact value is 4,294,967,296, or about 4.3 billion addresses, fewer than one per living person.
Source: IETF RFC 791; IANA
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