Structure of the BNB number

In MARC21 exchange records distributed by the British Library the BNB number appears in field 015$a, followed by $2bnb. The BNB number is a fixed length consisting of nine alphanumeric characters and is structured as follows.

Up to 1999

For BNB records created up to and including 1999 the structure is 'GByynnnnn' where:

  • ‘GB’ is a fixed literal GB
  • ‘yy’ is the last two digits of the year the record was created
  • ‘nnnnn’ is a running number starting at 00001 each year.


GB9801391 – Record number 1,391 created in 1998
GB9923456 – Record number 23,456 created in 1999

From 2000

From 2000 the structure of the BNB number is  'GBDyXnnnn' where:

  • ‘GB’ is a fixed literal GB
  • ‘D’ is an upper case letter acting as a decade counter e.g. A for 2000 to 2009, B for 2010 to 2019, etc.
  • ‘y’ is the actual 1-digit year within the decade e.g. A2 for 2002
  • ‘Xnnnn’ is a running number, right justified with zero fill, starting at 00001 each year, with ‘X’ being either numeric or alphabetic. If it is alphabetic then A represents 10, B represents 11, C represents 12, etc. The reason for this structure is to keep the total length of the BNB number within 9 characters, while fulfilling the need to assign more than 99,999 numbers in a single year.

In any one year the number assigned should run from GBDy00001 to GBDy99999 and then from GBDyA0001 to GBDyZ9999.


GBA000001 – Record number 1 created in 2000
GBA209865 – Record number 9,865 created in 2002
GBA5A0043 – Record number 100,043 created in 2005
GBA8C9913 – Record number 129,913 created in 2008 

Cataloguing-in-Publication (CIP) records

The structure of the BNB numbers assigned to Cataloguing-in-Publication (CIP) records is an exception to the above. Records created by the CIP agency used to be assigned a five character descending running number commencing Z9999 e.g. GBA2Z9954.

With the Library’s implementation of its integrated library system in June 2004, this practice ceased and since then CIP records have been assigned BNB numbers from the same sequence as records created in the Library.