Calculating the Check Digit
for a UPC
(Universal Product Code)
Assume the Number System Character is 'A', the Manufacturer’s Prefix is 'BCDEF', and the Item Code is 'GHIJK'. Calculate A + C + E + G + I + K, multiply that by 3, then add B + D + F + H + J. The check digit is how much you have to add to that number to make it a multiple of ten.
An example: The UPC 8 24563 00032 X, where X is the check digit that we don't know. We calculate (8 + 4 + 6 + 0 + 0 + 2) * 3 + (2 + 5 + 3 + 0 + 3) = 73. The check digit (X) is then 7, since we can add 7 to 73 and get a multiple of ten (80).