Understanding Mifare Unique Identifier (UID)

A unique identifier (UID) is a numeric or alphanumeric string that is associated with a single entity within a given system. UID make it possible to address that entity so that it can be accessed and interacted with. 

  • A UID is different from “serial number”  that UID is in Hexidecimal and a serial number is an integer number.


  • There are many ways on how to turn the array of bytes into an Integer. In particularly a 4 byte Mifare UID, the most common way “Little Endian” or “Intel” reading method, that is starting from byte 3 to byte 0,  and the converted decimal number matched the printed number on the card. 


Example : BYTE 0 = E4, BYTE 1 = 3A, BYTE 2 = C9, BYTE 3 = D2,

Little Endian reading = D2 C9 3A E4 (in hexadecimal),

Little Endian reading = 3536403172 (in decimal) using the calculator in Microsoft Windows 


  • UID is a common expression, defined in the ISO/IEC 14443-3. In some case, some terms like RID, NUID (FNUID and ONUID) are not unique. 


  • The 4-byte UID is also called “Single Size UID”. The 7-byte UID is also called “Double Size UID”. The 10-byte UID is also called “Triple Size UID”.  Mifare Classic starts with a 4-byte UID, but the number of chips produced far exceeds the 4 bytes number  (4,294,967,296) around 2012. The new Mifare Classic card is using 7-byte UID. 


  • UID is hard coded on EPROM of each Mifare card and cannot be changed 


  • UID can be used simply as an identifier in the Access Control application.


  • More importantly, UID is used in applications to avoid fraudulence such as smart card store value prepayment.


We provide service to print UID on each Mifare Card