IPv4 uses 32 bits, in the form of:
255.255.255.255
I suppose it depends on your datatype, whether you're just storing as a string with a CHAR type or if you're using a numerical type.
IPv6 uses 128 bits. You won't have IPs longer than that unless you're including other information with them.
IPv6 is grouped into sets of 4 hex digits seperated by colons, like (from wikipedia):
2001:0db8:85a3:0000:0000:8a2e:0370:7334
You're safe storing it as a 39-character long string, should you wish to do that. There are other shorthand ways to write addresses as well though. Sets of zeros can be truncated to a single 0, or sets of zeroes can be hidden completely by a double colon.
