What is a POSTNET Barcode and How Can You Decode It?

The Postal Service developed the POSTNET (POSTal Numeric Encoding Technique) barcode to encode zip code information on letter mail for rapid and reliable sorting by barcode sorters (BCSs). The POSTNET barcode can represent a five-digit ZIP Code (32 bars), a nine-digit ZIP+4 code (52 bars), or an eleven-digit delivery point code (62 bars).

The illustration below shows the basic format of a 5-digit zip code POSTNET barcode.



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Each digit of the zip code is represented by 5 bars, therefore a 5-digit zip code uses 25 bars to represent the numbers. However, whether it represents five-, nine-, or eleven-digit zip code information, the POSTNET barcode is always printed in a format that begins and ends with a frame bar, which appears as a full or tall bar. To ensure POSTNET accuracy during mail processing, a correction character, which is five bars, must be included immediately before the rightmost frame bar of all POSTNET barcodes. The correction character is always the digit that, when added to the sum of the other digits in the barcode, results in a total that is a multiple of 10. For example, the sum of the ZIP+4 barcode 12345-6789 is 45. Adding a correction character of 5 results in the sum of the 10 digits being a multiple of 10.

The basic elements of the POSTNET barcode are binary digits represented as full bars and half bars, which are also referred to as tall bars and short bars. A full bar represents the number 1 and a half bar represents the number 0.

Each code character is made up of five bars, which together represent a single numeric digit. Specific combinations of two full bars and three half bars represent the digits 0 through 9. Only the 10 combinations shown in the Code Elements illustration are valid code characters.These 10 combinations represent all possible combinations of two full bars and three half bars. Also, these combinations are central to POSTNET error recovery because the system interprets any five bars that contain a combination other than two full and three half bars as an error.

The weights of the digits are not the same as standard binary, where the values are 1, 2, 4, 8, and 16 from the least to the most significant digit. Instead, the digits are weighted as 0, 1, 2, 4, and 7. Except for zero, you can determine the numeric value of each valid combination of five bars by adding the weights of the two positions occupied by the full bars (1s). For example, the combination 01010 contains a full bar in the second position (weight 4) and in the fourth position (weight 1). Adding 4 and 1 yields 5, which is the assigned value of this combination. The only exception is the combination 11000, which has a total weight of 11 but is assigned a value of zero.




For more detailed information see the link below.

Related Links:
POSTNET Bar Codes - US Postal Service
Using Vision to Decode a POSTNET Formatted Barcode

Reader Comments | Submit a comment »

Excellent!
This article is concise and clear. Thanks!
- Ed Dorsey, SBCS. evdorsey@sbcs.com - Nov 5, 2009

Perfect answer
Exactly what I needed to interpret Postnet bar codes. After a printer got one place wrong and sent our mail halfway cross country, this is a big help to keep us and our printers straight.
- Lindsey McWilliams, Humboldt County Elections. lmcwilliams@co.humboldt.ca.us - May 3, 2007

Not Confusing or Inaccurate
This article is clear and concise. The part of the article that a previous critic did not read or understand is the 2 of 5 bars in each of the characters is used for correction. The whole 2 of 5 with a correction character design works like this: The scanner looks at each character (5 bars). If one character has only 1 tall bar, the correction character is used to determine the value of the missed character. It's not a perfect system because if there is more than 1 tall bar missing the mail piece would get rejected. It's time proven to be a very reliable method.
- M. Dinger. notarealemailaddress@hotmail.com - Oct 11, 2006

Excellent article greatly helped me for a class. One thing I would recommend would be to setup a flash or a java script program where there is a interactive approach to understanding the material to gain some hands-on experience.
- James - Oct 2, 2005

Confussing and inaccurate
The article does not explain why some digits have a 1 and others have a 0 for the weighting value of zero. The 7,4,2,1 part makes sense, weighting of zero?
- Roger. Rogbaker@mpinet.com - Jul 19, 2005

Decoding document commentary
Precisely the information for which I searched presented with minimal superfluous information and in an easily understood format. The only downside is that it was about number 18 on the search engine listing and I had to scan a few to get to it. I should find all information this easily!
- Louis Oberbeck, The Darkroom Plus. tdrp@juno.com - Jan 18, 2005