GS1-128 Barcode FAQ

What is GS1-128 barcode, checksum, data format, application identifier, labels, bar module size, & reading GS1-128 barcodes

What is GS1-128 barcode?

The GS1-128 barcode is a subset of the Code 128 barcode symbology.

By agreement between AIM and GS1, use of the Function 1 Symbol Character (FNC1) in Code 128 symbols in the first symbol character position following the start character has been reserved exclusively for the GS1 system. This extremely flexible symbology encodes element strings using GS1 Application Identifiers.

A sample GS1-128 barcode label with Application Identifier "01", and data message "09501101530003".

GS1-128 Basic Characteristics

GS1-128 barcode symbology has the following characteristics:

Encodable character set

  • The GS1 subset of International Standard ISO/IEC 646
  • Four non-data function characters. FNC2 and FNC4 are not used in GS1-128 barcodes.
  • Four code set selection characters (including single character code set shift).
  • Three start characters.
  • One stop character.

GS1-128 checksum digit

GS1-128 barcode has one mandatory symbol check character.

GS1-128 barcode size characteristics

  • The maximum physical length is 165.10 millimetres (6.500 inch) including Quiet Zones.
  • The maximum number of data characters in a single symbol is 48.
  • For a given length of data, the symbol size is variable between limits in X-dimension to accommodate the ranges in quality achievable by the various printing processes.

GS1-128 barcode structure

The GS1-128 barcode is made up as follows, reading from left to right:

  • Left Quiet Zone
  • The double character start pattern:
    • A start character (A, B, or C)
    • The Function 1 Symbol Character (FNC1)
  • Data (including the GS1 Application Identifier represented in character set A, B, or C)
  • A GS1-128 check digit
  • The stop character
  • Right Quiet Zone

GS1-128 Data Characters

GS1-128 FNC1 (The Function 1 Symbol Character)

To create a valid GS1-128 barcode, a FNC1 (Function Code 1) must be inserted after the start character.

The FNC1 character is not a visible character. It does not show in the human interpretation of your barcodes. Only barcode scanners read FNC characters.

GS1-128 Start and Stop characters

GS1-128 has three start characters (Start A, Start B, Start C) and one stop character

  • Start characters A, B and C define the corresponding code set to be used initially in the barcode symbol.
  • The stop character is common to all code sets.
  • The decoder SHALL NOT transmit start and stop characters.

GS1-128 barcode start character A

GS1-128 barcode stop character

GS1-128 check digit

The GS1-128/EAN-128 check digit SHALL be included as the last symbol character before the stop character.

The GS1-128 checksum digit SHALL NOT be represented in the human readable interpretation nor shall it be transmitted by the GS1 128 decoder.

GS1-128/EAN-128 check digit calculator formula

The GS1-128 check digit formula SHALL be calculated according to the following rules.

  1. Retrieve the barcode character value
  2. Each symbol character position is given a weight. The start character is weighted 1. Then, beginning on the left with the first symbol character following the start character, the weights are 1, 2, 3 and 4 to...n for all subsequent symbol characters up to, but not including, the symbol check character itself; n denotes the number of symbol characters representing data or special information in the symbol, exclusive of the start and stop characters and symbol check character.
  3. Each symbol character value is multiplied by its weight.
  4. The products of the calculations in step 3 are totalled.
  5. The sum of the products is divided by 103.
  6. The remainder derived from the calculation in step 5 is the symbol character value of the symbol check character.

A example: how to calculate GS1-128/EAN-128 check digit

The following content shows how to calculate the GS1-128 check digit value for the batch number (AI 10) 2503X using the GS1-128 barcode.

GS1-128 barcode data (10)2503X consists the following characters:
Start C, FNC1, 10 (GS1 Application Identifier), 25, 03, Code B X [check digit], Stop

Characters Start C FNC1 10 25 03 Code B X
Step 1: Character values 105 102 10 25 3 100 56
Step 2: Weights 1 1 2 3 4 5 6
Step 3: Products 105 102 20 75 12 500 336
Step 4: Sum of products       1150
Step 5: Divide by 103       1150 / 103 = 11
Remainder = GS1-128 check digit value       17

GS1-128 Barcode Dimension Size Requirements

GS1-128 minimum X-dimension

GS1-128 barcode minimum X-dimension is 0.495mm. Its recommended X-dimension is also 0.495mm.

GS1-128 maximum X-dimension

GS1-128 barcode maximum X-dimension is 1.016mm.

GS1-128 minimum height

GS1-128 barcode minimum height is 31.75mm. Its recommended barcode height is also 31.75mm.

GS1-128 maximum height

GS1-128 barcode maximum height is 33.75mm.

Quiet zone minimum size

The minimum width of the Quiet Zone to the left and right of the GS1-128 barcode is 10x.

GS1-128 maximum barcode length

The maximum length of any GS1-128 barcode must be within the following limits:

  • The length, including Quiet Zones, cannot exceed 165.10 millimetres (6.500 inches).
  • The number of encoded data characters SHALL NOT exceed 48.

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