UPC stands for Universal Product Code. This code is typically used to record point of sale transactions for consumer goods throughout the grocery industry. UPC-A format requires an 12 digit string. The left side digits are composed of the Company Identifier.  This number is supplied by the U.C.C.  The remaining digits identify the trade item (product or service). The last digit is a checkdigit.    Typically, the first 6  digits are assigned by request by the Uniform Code Council. The remaining digits are assigned by the user The encodation for the left and right halves of the regular symbol, including UPC characters, number system character and module check character, is given in the following chart. Note that the left-hand characters always use an odd number (3 or 5) of modules to make up the dark bars, whereas the right-hand characters always use an even number (2 or 4). This provides an "odd" and "even" parity encodation for each character and is important in creating, scanning and decoding a symbol.

Step 1: Designate the least significant digit position as odd.

        3 1 4 5 7 9 0 1 2 5 8
        O E O E O E O E O E O

Step 2: Sum all the digits in the odd (o) positions

        3 + 4 + 7 + 0 + 2 + 8 = 24

Step 3: Multiply the result by 3

        24 * 3 = 72

Step 4: Sum all the digits in the even (E) positions.

        1 + 5 + 9 + 1 + 5 = 21

Step 5: Add the result of Step 2 with the result of Step 4.

        72 + 21 = 93

Step 6: Subtract from the next higher multiple of 10.

        100 - 93 = 7.  

        In this example, the check digit is 7.