There are several answers to this question which explains why there is so much confusion regarding this issue. Each answer represents a solution using barcodes in different ways.
Answer 1: The numbers in most barcodes represent a numerical field in some company’s database.
Example: Company A has a warehouse full of items. Each item has an ID. The ID is represented in numbers. The ID can be a SKU number. Every time the company send or receives items, they want to show it in their inventory software. Instead of having to type the numbers in (which can cause many mistakes and is very time consuming) they print labels with barcodes on them. The barcode is a machine (i.e. computer) readable code. They use a scanner to read the barcode. The scanner communicates with the software application. It tells the software that an item with a particular SKU number has entered the warehouse.
Answer 2: This answer has everything to do with UPc codes. There are several types of UPC bar codes used for different purposes. The numbers in a UPC barcode represent several pieces of information about the product.
The Three versions of the UPC barcode are: A, D, and E.
1. Version A (the regular version) - is used to encode a twelve digit number.
2. Version E (the zero suppressed version) - is a six digit code used for marking small packages.
3. Version D (the variable length version) is not commonly used for package marking. It is used in limited special applications.
4. Both Version A and E may include either a 2 digit or a 5 digit supplemental encodation. These extra digits are primarily used on periodicals and books. Supplemental encodations are supported.
The first 6 digits of the UPC barcode:
The UCC assigns manufacturers an Identification number. This is a 6 digit code. So the first 6 digits of the UPC barcode is the manufacturer ID.
The first digit of the Manufacturer ID in the UPC code represents the market segment or type of products they manufacture:
1. Consumer products - start with 0, 1, 6, 7, 8, or 9.
2. Items sold by weight - starts with 2. This is also used for items used in warehouses and stores that are not sold to the public.
3. Pharmaceuticals start with 3.
4. Warehouse and store only purposes - starts with the number 4.
5. Manufacturer coupons, and store loyalty cards UPC numbers start with a 5.
Digits 7-12 of the UPC bar code:
Represent the item number. The item number is assigned by the manufacturer. It is their code for their item.
For items sold by weight - the first five middle digits are used to identify the item. The next five digits are used to identify weight or price, with the first digit of that set signifying whether it's for weight or price.
To help illustrate the difference between UPC and other bar codes look at this example:
I hope this helps clarify some of the confusion. As you can imagine there is more to UPC codes than meets the eye. As always if you have questions about a subject or just want me to explain some things about barcodes, labels and printing - drop me a line firstname.lastname@example.org.