Crystallographic Information Framework

Format of telephone/fax numbers

Many CIF data items take as value a telephone or fax number (e.g. _publ_contact_author_phone). The convention for expressing a telephone or fax number is as follows. A complete telephone or fax number may be defined by concatenating

  • the international dialling prefix
  • the area code in parentheses (without the area code initial digit as used for internal communications - see the first example below)
  • the local number
and optionally
  • the character "x" followed by an extension number
The convention in the Core dictionary version 1.0, where the international dialing prefix was given in parentheses and an extension was indicated by the string "ext" (e.g. '(44) 1244 342878 ext 212'), is no longer recommended for writing CIFs, but CIF readers should accept it.


The telephone extension of the COMCIFS Coordinating Secretary at Chester (area code 01244), UK (international code 44)
The fax number of the IUCr office in Chester, UK
A telephone number in France, where area codes are not supported