IntroductionThe POSTNET (Postal Numeric Encoding Technique) barcode was invented by US Postal Office to encode ZIP information. Having your letter printing system POSTNET capable enables you to receive a discount on the postage.
The US delivery address coding can be of three forms (1) 5-digit ZIP; (2) 5-digit ZIP + 4 code (3) 11-digit delivery point code. So a valid POSTNET barcode contains either 32 bars, 52 bars or 62 bars (including frame bars and check digit, see below).
POSTNET is a numeric symbology. Different from most other symbologies, POSTNET has requirement to the actual bar height and width. The information is encoded in the height and has nothing to do with the spaces.
Check Digit CalculationThe check digit is based on Mod 10 algorithm. The value of the check digit is that when added to the sum of other digits in the barcode, results in a total that is multiple of 10.
For example in the diagram above, the check digit for 91801 is 1 since 9+1+8+0+1+1=20 which is two times of 10.
Structure of a POSTNET symbolThe POSTNET barcode starts with a long bar (frame bar) and ends with a frame bar. Between these two frame bars is the encoded address information followed by a check digit. Each code character is made up of five bars, either long or short. If we use 1 to represent the long bar, 0 to represent the short bar, each character is encoded based on the table to the left.
POSTNET barcode should be placed in lower right corner of the envelope or in the address block as illustrated below. For more information, visit US Postal Office web site.