What is a POSTNET Barcode?

What are POSTNET Barcodes

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Efficiently sorting and delivering mail is crucial for the United States Postal Service (USPS) operations. To streamline this process, the USPS developed the POSTNET barcode, a symbol that encodes a ZIP Code, ZIP+4 code, or delivery point barcode (DPBC). 

The POSTNET barcode system was developed to speed up the sorting process and reduce the time postal carriers took to deliver letters. The USPS also used the PLANET symbology in conjunction with POSTNET for business and courtesy reply mail. 

However, in 2009, the USPS introduced the Intelligent Mail Barcode (IMB), eventually replacing both POSTNET and PLANET. 

In this article, we will explore what the POSTNET barcode is, how it worked, and why the more advanced IMB eventually replaced it.

What is a POSTNET Barcode?- Detailed view


POSTNET stands for Postal Numeric Encoding Technique. It is an important symbol developed by the United States Postal Service to reduce mail sorting time and improve efficiency. It is fixed length barcode symbology that can only encode numeric digits (0-9)

POSTNET codes consist of five, nine or eleven digits representing a ZIP Code, a ZIP+4 code, or a delivery point barcode (DPBC). They were used in conjunction with PLANET barcodes.

However, POSTNET codes were phased out in favour of the Intelligent Mail Barcodes (IMB) from 2009 onwards. IMB improved the mail tracking system, which enabled postal services to track, sort and direct mail more efficiently than ever before     

Although the POSTNET barcode symbology has been officially discontinued, it is still used for internal operations in various industries and businesses. 

What is a ZIP Code?

Properties and types of ZIP Code

A ZIP code is a structured number that helps identify an address when sending mail or packages. The acronym “ZIP” stands for Zoning Improvement Plan. It was invented by Robert Aurand Moon in the 1940s.

The U.S. Postal Service introduced the 5-digit ZIP code in 1963 as a way to make mail delivery more efficient. The 5-digit ZIP code consists of 5 digits. The first digit identifies the zone, followed by two digits that specify the metropolitan area or regional centre, and two more digits indicating the local post office or postal zone in larger cities. 

In 1983, USPS increased the size of ZIP codes from five to nine digits and called it ZIP+4 Code. This ZIP code was created by adding four extra digits for greater precision within a local post office area. 

Later, the USPS added two more digits creating an 11-Digit Delivery Point Code for even higher accuracy in delivering mail.

Formats of the POSTNET Barcode

Three formats of POSTNET Barcode

The POSTNET barcode can be in one of three ZIP formats: 5-digit ZIP code, 9-digit ZIP+4 code, or 11-digit Delivery Point Code. 

Let us learn about each format in detail.

5-Digit ZIP Code Barcode

The barcode for a 5-digit ZIP Code consists of 32 bars which include a frame bar. Out of 32 bars, 25 bars in this barcode represent the ZIP Code, 5 bars for the correction digit, and a final frame bar.

Features of 5 Digit ZIP Code
Characteristics of 9 Digit ZIP+4 Code

ZIP+4 Barcode

The ZIP+4 barcode is a field consisting of 52 bars. This barcode includes a start frame bar, 45 bars representing the proper ZIP+4 code for the address, 5 bars representing the correction digit, and a final frame bar.

Delivery Point Barcode

A Delivery Point barcode (DPBC) indicates a particular delivery point. To create a DPBC, you must add 10 bars to the ZIP+4 barcode. These 10 bars represent two additional digits of the code.    

 Please note that It’s crucial to obtain the accurate DPBC by utilising a CASS-certified delivery point code address matching process.

Five features of 11 Digit Delivery Point Code

Structure of the POSTNET Barcode

Six points on structure of POSTNET Barcode

The POSTNET barcode symbol comprises the following elements.

  • Leading quiet zone
  • Start bar, also called a frame bar (a single tall bar)
  • Message data (Encodes address information)
  • Check digit
  • Stop bar, also called a frame bar (a single tall bar)
  • Trailing quiet zone

The POSTNET encoding method uses bar heights to represent data in the barcode. Every numeric character in the barcode consists of five bars, out of which two are tall, and three are short. The width of all bars and spaces remains constant.

POSTNET barcodes consist of 32 lines, with the first and last being long lines that mark the beginning and end of the code. The remaining 30 lines are grouped into six groups of five lines each, where two long lines and three short ones represent a single numerical digit. By examining these patterns, it is possible to decipher which digits are represented by each group.

Quiet Zone

The quiet zone is a blank area that surrounds the POSTNET barcode image. You can set the quiet zones on the left, right, top, and bottom of the POSTNET barcode.

Frame Bar

The start and stop pattern of POSTNET barcodes is known as Frame Bars. It is represented by a single tall bar at the start and at the end of the POSTNET barcode.

Message Data

Message Data is a format used for encoding zip code addresses in a machine-readable way. There are three different lengths in which Message Data is encoded. 

  1. 5-digit POSTNET barcode: five digit zip code
  2. ZIP+4 POSTNET barcodes: nine digit zip code
  3. DPBC POSTNET barcode: nine digit zip code + two DPBC digits

Check Digit

POSTNET barcodes include a checksum digit, also known as a correction character, to ensure accuracy during decoding. This digit is calculated using the Modulo 10 method and is a single-digit number between 0 and 9. 

By verifying the checksum digit, the USPS can ensure that the POSTNET code has been accurately scanned and interpreted.

How to Design a POSTNET Barcode?

The United States Postal Service established some design guidelines for the POSTNET barcode system to ensure the accuracy and scannability of the code. These guidelines covered several aspects, including quiet zones, bar height, bar widths, and barcode density.

Design rules of quiet zones of POSTNET Barcode

Quiet Zones

A POSTNET barcode should have a 0.04 inches (1.02 mm) quiet zone above and below the barcode symbol. It should also have a 0.125 inches (3.18 mm) quiet zone at the start and end of the code.

Bar Height

The POSTNET barcode’s structure is composed of tall and short bars representing numbers, with each number being represented by two bars, one tall and one short. The bars’ correct heights are essential to ensure accurate readability. 

The height of the tall bars should be 0.125 inches (3.18 mm), with a tolerance of plus or minus 0.010 inches (0.25 mm). 

The height of the short bars should measure 0.050 inches (1.27 mm) in height, with a tolerance of plus or minus 0.010 inches (0.25 mm).

Design rules of bar height of POSTNET Barcode
Two design rules of bar width of the POSTNET Barcode

Bar Width

POSTNET barcodes are designed for use in automated mail sorting systems, and the widths of their bars and spaces are critical to ensure accurate decoding. 

The width of the individual bars should be between 0.015 inches and 0.025 inches (0.38 mm – 0.64 mm). 

The width of bar-space pairs should be between 0.045 inches and 0.050 inches (1.14 mm – (1.27 mm). Each bar and space pair has a barcode density of about four characters per inch.

Barcode Density

Barcode density is the number of characters a barcode can encode per inch.   

The POSTNET barcode has a very precise density range. The barcode should have 21 bars per inch, plus or minus one bar. This means that each inch of the barcode must have exactly 20 or 22 bars. Any deviation from this density range can result in inaccurate decoding.

Two design rules of barcode density of POSTNET Barcode
List of three design rules of positioning of POSTNET Barcode

How to Position a POSTNET Barcode?

USPS barcode scanners are programmed to locate and read barcodes in a specific envelope area. Therefore, to ensure successful scanning, you must correctly position the barcode within a particular area.

Here is how you should position a POSTNET barcode on an envelope. 

  • It should be 3.5 inches (88.90 mm) from the left edge.
  • It should be 4.25 inches (107.95 mm) from the right edge. 
  • It should be 0.25 inches (6.35 mm) away from the bottom (plus or minus 0.125 inches (3.18 mm)).  

How to Generate and Print a POSTNET Barcode?

While generating and printing a POSTNET barcode is no longer necessary, it can still be useful for directing mail or internal document-tracking applications. 

You can generate a POSTNET code using a free barcode generator or label designing and printing software like Seagull Scientific BarTender.  

It is strongly recommended to print the POSTNET barcode using thermal printers. This is due to the fact that thermal printers provide clear and accurate prints of the barcode, which ensures that it can be scanned quickly and accurately.


POSTNET barcodes were an important part of the USPS system, which helped to reduce the time and labour for sorting mail before delivery. Though POSTNET was replaced by IMB in 2009, it still remains a vital part of postal barcode history. 

The development of the POSTNET bar code symbol was key in improving efficiency across post offices around the country and is a good example of how technology can be used to improve traditional processes.

We hope this article was helpful.

Thanks for reading! 

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