How To Read Barcodes

Here is an example of a USPS POSTNET barcode that represents a ZIP of 38614 and a ZIP+4 of 5035 and a delivery point of 17 and a check digit of 7. The complete barcode decodes to 386145035177 which is a combination of the 4 parts.

1) Disregard the first bar and the last bar. These just mark the beginning and ending of the barcode and are not used to represent a number.

2) A combination of 5 "bars" represents each digit. We have 12 digits in 386145035177 so we'll need 60 bars. Read in groups of 5 bars and place the numbers 74210 under the bars, one number for each bar in each set of 5 bars.

3) Add each digit that appears under a tall bar. For the first set of 5 bars, the digits 2 and 1 appear under tall bars: 2 + 1 = 3. This set of 5 bars represents the number 3, which is the first digit in the complete barcode 386145035177.

4) Try the next one: 7 + 1 = 8. 
Then 4 + 2 = 6.
Then 1 + 0 = 1.
Then 4 + 0 = 4.
Then 4 + 1 = 5.

5) The next digit is a little trickier since it is an exception to the rule: 7 + 4 = 11. But 11 is a 2-digit number that is not allowed in a barcode. This is actually the representation for 0 (zero) and it is the only digit that does not follow the 74210 rule.

Try to decode the example direct mail POSTNET barcodes:

So you can read it, but how do you know it is correct? That's a little more difficult but we do know a little. Remember, the barcode is made up of 4 pieces: 5-digit Zip, Zip+4, Delivery Point, and Check Digit. You should all be familiar with the first 2 (Zip and Zip+4) and know how to locate them in the address block. If the first 9 digits of the barcode match the 9 digits of the Zip Code then you're off to a good start. 

As for the Delivery Point, that is a two digit number that narrows the delivery area of a mail piece. In most cases you can get the delivery point from the last 2 digits of the street address. For example, "630 Pennsylvania" might have a delivery point of 30. And "7 Park Place" might have a delivery point of 07. We say "might" because delivery points are actually assigned by the USPS and do not necessarily follow this standard. But this is enough to help you decide if the barcode your looking at is correct for the corresponding delivery address.

The check digit is arrived at by adding up the 11 digits and finding the number that you would add to make a multiple of 10. In the first example, 3 + 8 + 6 + 1 + 4 + 5 + 0 + 3 + 5 + 1 + 7 = 43. You would have to add 7 to this to get 50 which is the next multiple of 10. So 7 is the check digit. If you are printing a barcode from any type of computer, it would be extremely rare to have an incorrect check digit.

 

Here is a list of all 10 digits that you can print out and keep with you: