How many bits are there in Mac address?

48-bits. Probably so that there would be enough for every network device to have a worldwide unique address. This 48-bit address space contains potentially 2^48 or 281,474,976,710,656 possible MAC addresses. (2 to the 48th power.)

Which will probably also run out (some day?) like IPv4 is running out and will be supposedly fixed by IPv6 which has a larger address spac