POSTNET (Postal Numeric Encoding Technique) is a

barcode A barcode or bar code is a method of representing data in a visual, Machine-readable data, machine-readable form. Initially, barcodes represented data by varying the widths, spacings and sizes of parallel lines. These barcodes, now commonly ref ...

symbology A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise different concepts ...

used by the

United States Postal Service The United States Postal Service (USPS), also known as the Post Office, U.S. Mail, or simply the Postal Service, is an independent agencies of the United States government, independent agency of the executive branch of the federal governmen ...

to assist in directing mail. The ZIP Code or ZIP+4 code is encoded in half- and full-height bars. Most often, the

delivery point In a Mail, postal system, a delivery point (sometimes DP) is a single mailbox or other place at which mail is delivered. It differs from a address (geography), street address, in that each address may have several delivery points, such as an apart ...

is added, usually being the last two digits of the

address An address is a collection of information, presented in a mostly fixed format, used to give the location of a building, apartment, or other structure or a plot of land, generally using border, political boundaries and street names as references, ...

PO box A post office box (commonly abbreviated as P.O. box, or also known as a postal box) is a uniquely addressable lockable box located on the premises of a post office. In some regions, particularly in Africa, there is no door-to-door delivery ...

number. The barcode starts and ends with a full bar (often called a guard rail or frame bar and represented as the letter "S" in one version of the

USPS The United States Postal Service (USPS), also known as the Post Office, U.S. Mail, or simply the Postal Service, is an independent agency of the executive branch of the United States federal government responsible for providing postal serv ...

TrueType Font) and has a

check digit A check digit is a form of redundancy check used for Error detection and correction, error detection on identification numbers, such as bank account numbers, which are used in an application where they will at least sometimes be input manually. It ...

after the ZIP, ZIP+4, or delivery point. The encoding table is shown on the right. Each individual digit is represented by a set of five bars, two of which are full bars (i.e. two-out-of-five code). The full bars represent "on" bits in a pseudo-

binary code A binary code represents plain text, text, instruction set, computer processor instructions, or any other data using a two-symbol system. The two-symbol system used is often "0" and "1" from the binary number, binary number system. The binary cod ...

in which the places represent, from left to right: 7, 4, 2, 1, and 0. (Though in this scheme,

zero 0 (zero) is a number representing an empty quantity. Adding (or subtracting) 0 to any number leaves that number unchanged; in mathematical terminology, 0 is the additive identity of the integers, rational numbers, real numbers, and compl ...

is encoded as 11 in

decimal The decimal numeral system (also called the base-ten positional numeral system and denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers (''decimal fractions'') of th ...

, or in POSTNET "binary" as 11000.)

Encoding

The following table shows the encoding for decimal digits:

Example

The ZIP+4 of 55555-1237 yields a check digit of 2 for encoded data of 5555512372
Together with the initials and terminal frame bars, this would be represented as:

Barcode formats

There have been four formats of Postnet barcodes used by the Postal Service: A 5 digit (plus check digit) barcode, containing the basic ZIP Code only, referred to as the "A" code. 32 bars total. A 6 digit (plus check digit) barcode, containing the last 2 digits of the ZIP Code and the 4 digits of the ZIP+4 Code, referred to as a "B" code. 37 bars total. In the early stages of Postal automated mail processing the B code was used to "upgrade" mail that had been coded only with a 5-digit "A" code. This barcode was only found on mail that received a 5-digit barcode on the initial coding by an OCR. Now obsolete. A 9 digit (plus check digit) barcode, containing the ZIP Code and ZIP+4 Code, referred to as the "C" code. 52 bars total. The 9-digit barcode enabled the sorting of mail to the individual delivery carrier, and in some cases into a semblance of delivery sequence. An 11 digit (plus check digit) barcode, containing the ZIP Code, ZIP+4 Code, and the

code. 62 bars total. This is usually referred to as the DPBC, or Delivery Point Bar Code. By including delivery point information, it enables the Postal Service to sort mail into delivery point (address) sequence.

Discontinuation

The POSTNET 11-digit barcode was the predominant postal addressing barcode in use until the Intelligent Mail barcode (also known in its early usage as OneCode Solution) was introduced and implemented. The POSTNET barcode was replaced by the Intelligent Mail barcode in the fall of 2009, combining all previous Postal Service barcodes and marking into a single barcode. The Intelligent Mail barcode was originally supposed to be required beginning May 2011 however the USPS postponed the requirement date, allowing mailers to continue receiving automation discount rates using the POSTNET barcode until January 28, 2013, at which time Intelligent Mail barcode was required for those reduced rates.

Checkdigit algorithm

The check digit is chosen so that the sum of all digits in the bar code is a multiple of 10. Equivalently, the

modulo In computing and mathematics, the modulo operation returns the remainder or signed remainder of a division, after one number is divided by another, the latter being called the '' modulus'' of the operation. Given two positive numbers and , mo ...

-10 sum is 0. To calculate the check digit: #Add up the digits. For example, if a letter is sent to Young America, Minnesota, it might be sent to 55555-1237, which would have the sum of 38. #Find the remainder of this number when it is divided by 10, in this case 8. This is also known as the sum modulo 10. A simple way to combine the two steps is to sum the digits without a tens column at all, but discard all carries. #Subtract the sum modulo 10 from 10. Continuing with the example, 10 − 8 = 2. The check digit is therefore 2. If calculated correctly, the sum of the ZIP, ZIP+4, or ZIP+4+delivery point digits and the check digit will always be a multiple of 10. Continuing with the example above, (5+5+5+5+5+1+2+3+7+2) = 40, and 40 mod 10 = 0. Note that the

Delivery Point In a Mail, postal system, a delivery point (sometimes DP) is a single mailbox or other place at which mail is delivered. It differs from a address (geography), street address, in that each address may have several delivery points, such as an apart ...

is often added after the ZIP+4 and before the check digit, in which case the computation of the check digit includes the ZIP+4 ''and'' the Delivery Point.

References