The UPC-A barcode is the most common and well-known symbology in the United States.

You can find it on virtually every consumer goods in your local supermarket, as well as books, magazines, and newspapers.

There are a number of UPC variants, such as UPC-E, UPC 2-digit Supplement, UPC 5-digit supplement.

UPC-A encodes 11 digits of numeric data along with a trailing check digit, for a total of 12 digits of barcode data.

The human-readable digits are printed for the benefit of us lowly humans only. Obviously, the scanner doesn't pay any attention to them whatsoever and a barcode that is printed without these numbers will work just as well as one that includes them.

A UPC-A number consists of four areas:
1. The Number System;
2. The Manufacturer Code;
3. The Product Code;
4. The Check Digit.

Normally the number system digit is printed to the left of the barcode, and the check digit to the right. The manufacturer and product codes are printed just below the barcode, separated by the guard bar.

Number System

The number system is the first digit in the UPC number to identify the type of the product. For example, if the barcode starts with digit 5, this barcode is a coupon code.

NS	Description
0	Regular UPC codes
1	Reserved
2	Weight items
3	Durg/Health items
4	In-store use on non-food items
5	Coupons
6	Reserved
7	Regular UPC codes
8	Reserved
9	Reserved

Manufacturer Code

The manufacturer code is assigned by UCC council to each manufacturer or company which distributed goods that uses UPC-A barcode. To apply for a manufacturer code, visit www.uc-council.org. Note that UCC has started to assign manufacturer code longer than 5 digits to conserve the numbering resource.

Product Code

The product code is assigned by the manufacturer. The product code is a 5-digit number so it can accommodate 99,999 possible product codes for each manufacturer. That is far enough for any manufacturer in the world!

Check Digit

The check digit is used to verify that the barcode is generated or scanned correctly. The check digit is calculated based on the rest of the barcode digits. Read the following section to learn how to calculate the check digit.

The nominal X dimension is 13 mils. The printable X dimension ranges from 10.4 to 24 mils.

The coupon code is a UPC code with number system 5.
A coupon code contains four areas:
1. Number System 5
2. Manufacturer Code
3. Product Family code and value code
4. Check Digit

UPC-A check digit is calculated using standard Mod10 method.
Here outlines the steps to calculate UPC-A check digit:
1. From the right to left, start with odd position, assign the odd/even position to each digit.
2. Sum all digits in odd position and multiply the result by 3.
3. Sum all digits in even position.
4. Sum the results of step 3 and step 4.
5. Divide the result of step 4 by 10.

The check digit is the number which adds the remainder to 10.

A UPC-A symbol can be divided into two halves, each consisting of six digits separated by a center guard bar pattern. The whole symbol is surrounded by two guard bar patterns. The same digit has different encoding depends whether it is in the left halve or in the right halve.

The encoding pattern for digits in the left halve always starts with a space while the one for digits in the right halve always start with a bar and ends with a space.

A UPC-A symbol has the following structure:
1. Start guard bars, always with a pattern bar+space+bar
2. Left halve, six digits encoded using the encoding schema A or B
3. Center guard bars, with a pattern space+bar+space+bar+space
4. Right halve, six digits encoded using the encoding schema C
5. Stop guard bars, always with a pattern bar+space+bar