In numbers with five or more digits, Anglo-American usage dictates that there be commas before groups of three digits, counting from the right, except for a group of three digits at the beginning of the number.
Customers reported a total of 212,413 hardware malfunctions.
Use commas to separate adjacent numbers.
In 1994, 212 cases had been diagnosed.
Use commas to separate items in an address.
Einstein then moved to Princeton, New Jersey.
Use commas to set off the year in dates expressed in the month-day-year sequence.
Greenberg began the project on July 2, 1992.
Omit commas when only the month and the year are stated.
Greenberg began the project in July 1992.
In dates written in the day-month-year sequence, the comma is omitted.
Greenberg began the project on 2 July 1992.
Use commas to separate certain elements or subelements of a bibliographic group in a reference list or bibliography if called for by the documentation style you are following.
Smith, P. R., B. Coleman, and I. Waitz, "The Redesign of O-Ring Seals."
In representing normal human karyotypes and chromosomal aberrations, place a comma between the total number of chromosomes and the X and Y symbols for sex chromosomes.
46,XX[normal female karyotype]
46,XY[normal male karyotype]
49,XXXY[Triple X Syndrome]
In chemical formulas, use commas to separate letters and numbers identifying the location of an atom or group in a molecule.