How UPC Barcodes Work

Ever wonder how the UPC, Universal Product Code, found on nearly everything bought nowadays really work? These codes begin with a company called the Uniform Code Council that charges an annual fee for a manufacturer to enter the UPC system. The Uniform Code Council issues the manufacturer an identification number and provides guidelines for using it. All UPC bar codes include the manufacturer’s six-digit identification number among the standard twelve-digit UPC code. UPC symbols printed on packages have two parts, the machine-readable bar code and the human readable 12-digit UPC number.

Looking at a UPC bar code, the first six digits of the UPC number are the manufacturer’s identification number. When looking at these manufacturer’s codes, notice that the large manufacturers have manufacturer ids with lots of zeros in them, such as Post whose number is 043000 and General Mills, whose number is 016000. These manufacturer id numbers are often suppressed by leaving out the zeros, and making the UPC bar code only an 8-digit number instead of a 12-digit number. The five digits following the manufacturer’s id number are the item number. The UPC coordinator who is an employee of the manufacturer assigns the item number. The UPC coordinator has to make sure the same code is not already in use on another product, remove any retired codes from the product line, etc. Every item the manufacturer sells, as well as every size package and every repackaging of the item has to have a different item code, and it is the responsibility of the UPC coordinator to keep all of these numbers straight. The very last digit of the UPC code is the check digit. This digit allows the scanner to determine if the accuracy of the number scanned. There are five steps used to determine this check number:
Step one: add all the digits in the odd positions together
Step two: multiply the sum from step one by 3
Step three: add all the digits in the even positions together and add this
Step four: add the sum of step three to step 2
Step five: determine the number needed to add to the sum found in step four to create the nearest multiple of 10, this number needed is the check number.
This calculation is performed each time the scanner scans an item. The item will be rescanned if the scanner does not get the same number after doing the calculations.

The bar code does not have the price of the item in it at all. The store determines the price of the item. After scanning the item, the cash register sends the UPC bar code information to the store’s central point of sale computer where it locates the code and then the central computer sends the price of the item back to the cash register right then. This allows the store to set the price of the item instead of the manufacturer. If the bar code included the price, the store would have not control over the price and therefore would not be able to have sale prices, but they would also not be able to commit scanner fraud.