Spatula Systems - Nick Johnson's Barcode Specifications

Extrapolated Barcode Specs

Compiled by Nick Johnson.

POSTNet

These are the nifty barcodes we see on the bottoms of envelopes and around the addresses on bulk mail. The theory is that these allow the postal service to deliver mail in 72 hours instead of 3 days. These codes are actually binary coded with an even number of tall bars guaranteed by the last bar for each character (parity bit, if you will, so we have even parity). I've been told that this is really just a code 2 of 5 scheme that happens to look like a BCD/parity code. This code differs from the others in that it is not based on the width, but rather the height of the barcodes. It is also more anal about the spacing of the bars; there are supposed to be 22 bars to the inch. The tall bars are about 1/10 of an inch high, and the short bars are about half that height at 1/20 of an inch.

Here is a table of the postnet number codes:

Digit Code
0 11000
1 00011
2 00101
3 00110
4 01001
5 01010
6 01100
7 10001
8 10010
9 10100

Digit	Code
0	11000
1	00011
2	00101
3	00110
4	01001
5	01010
6	01100
7	10001
8	10010
9	10100

Astute observers may notice that when we got to 7, we skipped our binary value to 8. This is because the code for 7, which would have been 01111, would require 4 1's, whereas every other digit is represented by no more than 2 1's. So, probably for simplicity in the scanners, 7 was skipped and the binary value for 8 was assigned to the digit 7. 8 is assigned 9, 9 is assigned 10, and 0 is assigned 12 (skipping 11 for similar reasons). This makes the barcode conform to a code 2 of 5 scheme.

Postnet codes have a trailing checksum that is the Modulo 10 of the sum of the digits. So to get the checksum, add all the digits in the zip code and subtract that sum from the next multiple of 10. The checksum for 32501 would be 9 (3+2+5+0+1=11; 20-11=9).

For Bulk Rate mail, the first two digits of the recipient's street address are appended to the zip+4. For example, for the address 65535 Long Street, San Francisco, CA 94123-5678 the whole code would be 94123567865.

Return address:
To address:
To Zipcode:

Fill in a zip code and get a Postnet barcode:

Fill in a return address, to address, and to zip code, and get a business-sized envelope. Assumes 72 pixels per inch for printing.

Codabar	Code 2 of 5	Code 3 of 9	Interleaved 2 of 5
Postnet	UPC	Code 128	Code 16k


Thu Jul 24 11:02:13 PDT 2008		barcode/postnet.src
Updated: Thu Aug 18 2005 9:31.35		Viewed: never