A universally unique identifier (UUID) is a 16-byte (128-bit) number. Therefore, the number of possible UUIDs is 1632, or about 3.4 × 1038. In its canonical form a UUID is expressed by 32 hexadecimal digits divided into five groups separated by dashes of the form 8-4-4-4-12 giving a total of 36 characters (32 digits and 4 dashes). For example: FFDD94ED-0339-44B8-AAF1-305B7C24435C
A UUID version 4 is randomly generated. As with other UUIDs, four bits are used to indicate version 4, and 2 or 3 bits to indicate the variant (10 or 110 for variants 1 and 2, respectively). Therefore, for variant 1 (i.e. most UUIDs) a random 4 UUID version will have 6 variant bits and default version, leaving 122 bits for the randomly generated part, for a total of 2122 possible combinations.