Code 128 Barcode Explained

Code 128 Example

Code 128 was developed by Computer Identics in 1981 and has become very popular over the years. A Code 128 barcode symbol can encode letters, digits and control characters (TAB, ENTER etc.) which makes it very versatile and suitable for many applications. Today, Code 128 is one of the most widely used barcode types, for example for warehouse management, in the transport industry (e.g. by UPS or DHL) and in retail.

Contents:

  1. Code 128 at a glance
  2. Code 128 specifications
  3. Code 128 sub types and start / stop characters
  4. Code 128 Auto
  5. Accented, diacritic characters with Code 128
  6. Maximum length of Code 128
  7. Code 128 bit pattern
  8. Code 128 check digit calculation
  9. Code 128 sample barcodes
  10. Code 128 vs Code 39
  11. Code 128 vs EAN
  12. Code 128 on Amazon FBA labels
  13. Code 128 barcode fonts
  14. Decoding Code 128
  15. Creating Code 128 in Adobe Illustrator, InDesign
  16. Create Code 128 with a stand-alone barcode generator
  17. Bulk creating Code 128
  18. Creating Code 128 with Node JS, Python, C#, PHP, Java, Swift

Code GS1-128 is an application of Code 128 which encodes a GTIN-12, GTIN-13 or GTIN-14 plus supplemental data like best-before dates or batch numbers. See Code GS1-128 for a discussion of GS1-128 but read this page first.

Code 128 at a Glance

  • Type: Linear barcode symbology
  • Applications: Warehousing, transport, logistics, retail
  • Character set: Encodes all 128 characters from ASCII set
  • Modes: Control characters, alphanumeric, numeric compaction
  • Check digit: Modulo 103 (not mandatory but recommended)
  • Generators: Stand-alone, barcode fonts, barcode extensions
  • Scanning: CCD / Laser scanners, imagers, scanner apps
  • Printing: Thermal direct, thermal transfer, laser, inkjet, dot-matrix

Code 128 Specifications

Code 128 is standardized, the respective document is ISO/IEC 15417:2007, which can be obtained from ISO. As the code is rather old, the Code 128 specs are freely available online, for example in the Wikipedia article on Code 128.

Code 128 code sets A, B, C and start characters

Three different code sets or sub types are defined for Code 128 (namely Code 128 A, Code 128 B, and Code 128 C) that determine how the code is interpreted by the barcode scanner. The code sets differ in compactness and encodable character set.

Code 128 A: Partial ASCII set, no lower case, but ASCII control chars (TAB, CR/LF etc.)
Code 128 B: Full ASCII set, no ASCII control chars
Code 128 C: Only digits 0-9, encoded in pairs, very compact code

The code set to use is indicated to the scanner by the start symbol or start character. Also available are various mode switching or shift characters to switch from one set to another within a barcode symbol. Usually the sub type selection and switching within a symbol is handled by the barcode software that creates the code.

For reference we are including the bar patterns of the three start- and the single stop-character here. When using a Code 128 barcode font in Excel or similar applications, the start and stop characters will be mapped to certain character positions; however, the mapping is not standardized and will vary from font to font.

Code 128 A start character (bitpattern/widths: 211412, bar-gap-bar-gap-bar-gap, widths add up to 11):

Code 128 A Start Character

Code 128 B start character (widths: 211214):

Code 128 B Start Character

Code 128 C start character (widths: 211232):

Code 128 C Start Character

Code 128 stop character (widths: 311123):

Code 128 Stop Character

Code 128 Auto

Code 128 Auto refers to the automatic selection of the 128 subtype depending on the encoded data. This is performed by the respective barcode software to minimize the size of the code. Code 128 Auto is not a separate version or subset of the code.

Accented, diacritic characters, emoji with Code 128

In principle non-ASCII characters like German umlauts (e.g. "Ä Ö Ü") or accented characters (e.g. "á ñ ò") can be encoded in a Code 128 symbol by using a special character (FNC4), defined for Code 128 A and Code 128 B. However, this feature is not widely supported and cumbersome to use. Using a 2D barcode symbology like QR or Data Matrix with dedicated support for non-ASCII or Unicode data might be a better choice.

Code 128 maximum length

Code 128 is a variable length code, which in principle can encode an arbitrary length of data. The practical content limit for Code 128 is at 30 characters (large cap and small cap letters) or a maximum of 60 digits (purely numeric code).

Code 128 B with 30 characters, module width 0.3mm, total length c. 135mm (click for full size):

Code 128 Maximum Length Letters

Code 128 C with 60 digits, module width 0.3mm, total length c. 135mm (click for full size):

Code 128 Maximum Length Numeric

Note that many barcode scanners or reader apps have soft limits below those numbers. Also, a barcode must not be wider than the "reading window" or aperture of a scanner or it won't be scanned.

Code 128 bit pattern

Please see this post for the Code 128 bit pattern.

Check digit calculation for Code 128

Code 128 uses a Modulo 103 checksum algorithm. All characters of a symbol are added up and modulo divided by 103. The remainder is the checksum. For a sample calculation, see the Wikipedia article on Code 128.

The barcode software that generates the code will usually calculate the check digit automatically. The check digit can be any character from the code set, including non-printable characters like TAB or EOT. It is therefore not common to append the check character to the readable text under the code, likewise it is usually not transmitted by the scanner with the encoded data (check your scanner's manual for settings regarding Code 128).

In principle, Code 128 can be created without a check digit. However, all recent barcode scanners or scanner apps will expect a symbol to carry a check digit. This has implications when using a Code 128 barcode font, for example in Excel or Google Sheets, see below.

Sample Code 128

Purely numeric data, resulting in a Code 128 C symbol (compare the first three bars to the start characters listed above):

Example Barcode Code 128 C (numeric compaction)

Mixed data, resulting in a Code 128 B full ASCII symbol. Also note that this code is wider than the previous example although fewer characters are encoded:

Example Barcode Code 128 B (alphanumeric)

Mixed data ("ABC<TAB>DEF>"), resulting in a symbol that starts as Code 128 B to encode "ABC", then shifts to Code 128 A to encode the <TAB>, then back to 128 B to encode "DEF":

Example Barcode Code 128 A (control characters)

Note: The TAB is not shown in the textline, same goes for other non-printable characters.

When scanning this code, the barcode scanner will put out "ABC", followed by the <TAB>, then "DEF". This can be very useful: Consider a data entry mask with two text fields. The <TAB> can be used to move the input focus from one field to the next. The first part of the code ("ABC") would go into the first field, the second part ("DEF") would go into the second field.

The result can also be seen when decoding the code with Google Zxing, here the TAB is actually expanded:

Code 128 A Decoder TAB Character

Non printable characters (like the <TAB> above) are entered into our Code 128 generators using the tilde notation: You enter the tilde, followed by the three digit ASCII code of the symbol. E.g. to encode a <TAB> into the code you would enter "~009". For the code above the full entry string would read: "ABC~009DEF".

Code 128 vs Code 39

Another popular choice to encode alphanumeric characters is Code 39. The biggest advantages of Code 39 is that it can be used without a check digit. On the negative side, the barcode will only natively encode capital characters ("ABC"); small caps ("abc") can be encoded with Code 39 Extended but this code can get very large, as the following example illustrates (Code 128 top, Code 39 bottom):

Code 128 vs Code 39

Likewise, Code 39 does not support compact numerical symbols like Code 128 C and is generally a bad choice for larger amounts of data. For more info see Code 128 vs Code 39.

Code 128 vs UPC / EAN

UPC and EAN will only encode numbers while Code 128 can also encode letters (large cap and small cap) and a variety of special characters. In addition, EAN and UPC are fixed length codes: They only encode exactly twelve (UPC-A, GTIN-12) or thirteen (EAN 13, GTIN-13) digits. For more about EAN, see EAN 13 Explained.

Amazon FBA Barcodes (ASIN, FNSKU)

With FBA (Fulfillment by Amazon), two different types of barcodes are used:

  • Retail barcodes (EAN, UPC, ISBN) are used for new (i.e. unused) products and are the standard way of labelling products for which you are either a reseller, the manufacturer or brand owner and that are shipped via Amazon fulfillment. Those barcodes are called "Manufacturer barcodes" in Amazon speak.

    Amazon says: "When more than one seller has inventory with the same manufacturer barcode, Amazon may fulfill orders with the inventory that is closest to the customer, for faster delivery." This is called commingling. Commingling has implications when items are returned, if there is a warranty claim and with regard to VAT (in Europe) or sales tax (in the US).

  • FBA products without an EAN / UPC / ISBN code or items that are used or perishable are labelled with an "Amazon barcode". This is a unique Code 128 barcode that encodes either the product's ASIN or its FNSKU (for Fulfillment Network Stock Keeping Unit). The FNSKUs link a product to a seller and are preferrable if one wants to avoid commingling. FNSKUs are automatically assigned once a product is listed by a seller; the respective barcode labels can be printed directly from the seller's dashboard or downloaded as PDF for later printing.

    Here's an example of an FNSKU label on a product package (product):

    Amazon FNSKU Code 128 Barcode Label

    The Code 128 starts with the "128 B" subtype for encoding the initial "X", then switches to subtype "C" for the six digits "001069", then back to "B" for the rest.

    An identical Code 128, created with Softmatic BarcodePlus V5 (see below):

    Amazon Code 128 FNSKU Generator

    When using an FNSKU label with a product that already has an manufacturer barcode (EAN etc.), this barcode must be covered or removed to avoid mixups in the receiving department; the usual practice is to simply stick the FNSKU label over the EAN.

More here.

Code 128 font for Excel or Google Sheets

Code 128 is a good choice for embedding barcodes in your spreadsheet. Applications include catalogs with article numbers, serial numbers or GS1 data points like GTIN or best-before dates. The easiest and most straight forward way of creating Code 128 barcodes in Excel or Google Sheets is with a Code 128 barcode font. In order to support the different subtypes of Code 128 and the mandatory check digit, such a barcode font can only be used in conjunction with an add-in, for example the Softmatic barcode add-in for Excel.

This screenshot shows the add-in panel with a column of cells containing sequential Code 128:

Code 128 font in Excel

Note, that it is not sufficient to simply select the cell with your data and change the font to "Code 128" (a common misconception with the Libre Code 128 barcode font). This will not create a valid barcode because start-/stop-characters and the mandatory check digit are missing. Usually a Code 128 font for Excel will come with an add-in or macro to generate the required start and stop characters and the check digit. The macro or add-in will also format the data for the most appropriate Code 128 subtype.

More info • Download

Code 128 Decoder

Manually decoding Code 128 is possible, beginning with the start symbol and going forward one character or pair of digits at a time. A Code 128 decoder will also have to take mode switching and shift characters into account. Finally, the validity of the decoded data has to be verified against the Modulo 103 check digit. A reference decoding algorithm can be found in the GS1 General Specifictations, section 5.4.5 (download from GS1).

It's much more convenient though to use an app or an online service:

Result of decoding Code 128 barcode

Image shows the output for the above sample of Code 128 C (encoded data: "1234567890"), using Google Zxing, a free online decoder for Code 128. The "Raw bytes" section of the decoded result consists of eight bytes. The first and last bytes are the start and stop characters. In between are five bytes with the actual data (recall that Code 128 C encodes pairs of characters, i.e. "12", "34", "56" etc.) and the checkdigit.

If you want to try for yourself, here is a 300dpi version of the sample code.

Scanning Code 128

It is safe to assume that all barcode scanners available today will read Code 128 barcodes. However, there are some pitfalls and caveats when scanning Code 128; see here if you have a Code 128 symbol that can not be scanned.

With modern smartphones, dedicated scanner apps can be used to detect, read and decode barcodes like Code 128.

Video shows the CoScan app, a free PDF and barcode scanner for iPhone. The barcodes (EAN 13, Code 128 and QR) are correctly identified and decoded in the life image:

AppStore (free download)

Create Code 128 in Illustrator, InDesign

Easy to use barcode plug-ins and extensions for Adobe InDesign, Illustrator und Photoshop. For more videos, see the Softmatic Youtube Channel

The Softmatic barcode plug-ins and extensions for InDesign, Illustrator and Photoshop are available from the Softmatic online store.

Code 128 Generator

Softmatic BarcodePlus V5 creates Code 128 and will export the barcode as PDF / SVG (resolution-independent vector) oder raster image (PNG, TIFF). The app will automatically select the appropriate 128 subtype:

Softmatic BarcodePlus Code 128 Generator

Create Code 128 in bulk

For batch creation of Code 128 and Code 128 GS1, use Softmatic BarcodeFactory V5. The software will create thousands of barcode symbols in seconds, with data coming from the built-in serial number generator, the clipboard or via import from Excel, Numbers or CSV text files: