barcode (or bar code)

What is a barcode?

A barcode (sometimes seen as two words, bar code) is the small image of lines (bars) and spaces that is affixed to retail store items, identification cards and postal mail to identify a particular product number, person or location.

The code uses a sequence of vertical bars and spaces to represent numbers and other symbols. A barcode symbol typically consists of five parts: a quiet zone, a start character, data characters (including an optional check character), a stop character and another quiet zone.

How barcodes work

The barcode is simply an image. To become meaningful, a barcode reader, or scanner, must decode it. The reader uses a laser beam that is sensitive to the reflections from the line and space thickness and variation. The reader translates the reflected light into digital data that is transferred to a computer for immediate action or storage.

Readers may be attached to a computer, as they often are in retail store settings, or separate and portable, in which case they store the data they read until it can be fed into a computer.

Here are common uses for barcodes:

  • By supermarkets and retailers to track items sold and inventory
  • By libraries to identify and track borrowed books
  • By manufacturers and shippers to track product movements
  • By employers to verify and track employee working hours
  • By hospitals to identify patients
  • By marketers to tabulate the results of direct mail marketing returns
  • By researchers to track honeybees (using tiny barcodes)

Barcode standards

There is no one standard barcode. Instead, there are several different barcode standards called symbologies that serve different uses, industries, or geographic needs.

Since 1973, the Uniform Product Code (UPC), regulated by the Uniform Code Council, an industry organization, has provided a standard barcode used by most retail stores. The European Article Numbering system (EAN), developed by Joe Woodland, the inventor of the first barcode system, allows for an extra pair of digits and is becoming widely used. POSTNET is the standard barcode used in the United States for ZIP codes in bulk mailing.

The following table summarizes the most common barcode standards.

Barcode standard Uses

Uniform Product Code (UPC)

Retail stores for sales checkout; inventory, etc.

Code 39
(Code 3 of 9)

Identification, inventory and tracking shipments


Encoding zip codes on U.S. mail

European Article Number (EAN)

A superset of the UPC that allows extra digits for country identification

Japanese Article Number (JAN)

Similar to the EAN, used in Japan


Based on ISBN numbers and used on book covers

ISSN barcode

Based on ISSN numbers, used on periodicals outside the U.S.

Code 128

Used in preference to Code 39 because it is more compact

Interleaved 2 of 5

Used in the shipping and warehouse industries


Used by Federal Express, in libraries, and blood banks

MICR (Magnetic Ink Character Recognition)

A special font used for the numbers on the bottom of bank checks


The optical character recognition format used on book covers for the human readable version of the ISBN number


Used for the human readable version of the UPC, EAN, JAN, Bookland, and ISSN barcodes and for optional human-readable digits with Code 39 and Interleaved 2 of 5 symbols


Used by the United Parcel Service


A 2D type of barcode that can encode up to 1108 bytes of information; can become a compressed, portable data file (which is what the "PDF" stands for)

This was last updated in November 2022

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