A MAC address should not be confused with a [[MAC|message authentication code]] A MAC address is a 48-bit number that tends to address physical hardware, though it can be virtualised. Given that human beings struggle to comprehend binary numbers, we tend to write them as 12-digit hexadecimal numbers. As below, note that when we change the base we change the length as well. $2^{48} \equiv 2^{(4\times12)}\equiv16^{12}$