The numbering of European standards follows a well structured and organized sequence:

EN 50225:1996 (the year of availability of the EN is separated from the number by a colon)
EN 50157-2-1:1996 (the part number is indicated by a hyphen)

The first two numerals indicate the origin of the standard:

- 40000 to 44999 cover domains of common CEN/CENELEC activities in the IT field
- 45000 to 49999 cover domains of common CEN/CENELEC activities outside the IT field
- 50000 to 59999 cover CENELEC activities
- 60000 to 69999 refer to the CENELEC implementation of IEC documents with or without changes

The IEC and the ISO have allocated themselves blocks of publication numbers: from 1 to 59999 for ISO and from 60000 to 79999 for the IEC.