19 digits. The coding rules of access control ic card are composed of 19 digits, and the specific coding format is as follows: 2 digits are provincial codes, 2 digits are years, and the last two digits of the actual year are taken, for example, 09 is 2009. There is a long string of numbers on the card surface, most of which are ID cards, white cards or keychain cards, which can be distinguished by observing the numbers on the card surface.