The "UPC-A bar code" is by far the most common and well-known symbology, at least in the United States.
An UPC-A bar code is the bar code you will find on virtually every consumer good on the shelves of your local supermarket,
as well as books, magazines, and newspapers.
It is commonly called simply a "UPC bar code" or "UPC Symbol."
UPC-A barcode can encode numeric data from 0 through 9.
An UPC-A bar code is divided into four areas:
UPC-A encodes 11 digits of numeric (0 through 9) message data along with a trailing check digit, for a total of 12 digits of bar code data.
The UPC-A number system is a single digit which identifies the product type, if you will, that the following symbol represents.
The table below indicates what each number system identifies.
| Number System | Description |
| 0 | Regular UPC codes |
| 1 | Reserved |
| 2 | Weight items marked at the store |
| 3 | National Drug/Health-related code |
| 4 | No format restrictions, in-store use on non-food items |
| 5 | Coupons |
| 6 | Reserved |
| 7 | Regular UPC codes |
| 8 | Reserved |
| 9 | Reserved |
The UPC-A checksum digit is based on a modulo 10 calculation based on the weighted sum of the values of each of the digits
in the number system, manufacturer code, and product code.
The steps for calculating the check digit are as follows: