UPC Check Digits
A check digit (also called a ‘check sum’) is a number appended to the data contained in a barcode. Check digits are used to assure accuracy; to “check” for errors. They typically consist of a single digit computed from the other digits in the data.
All UPC (Universal Product Code) bar codes include a modulo-10 check digit. The UPC check digit is the twelfth digit, located to the far right of the UPC number, below the bars and spaces. While every complete UPC number contains twelve total digits, only the first eleven numbers are based on user data. The 12th and final digit is always the UPC check digit.
Calculating the UPC check digit requires an unusual algorithm (mathematical rule or procedure). While most people prefer to utilize our UPCTools software to calculate the UPC check sum, it is possible to work it through on paper.
Want to give it a try? Grab a pencil!
Our example barcode data is 41234554321.
- dd the digits in the odd-numbered positions (first, third, fifth, etc.) together and multiply the total by three.
4+2+4+5+3+1=19 19x3=57 - Add the digits in the even-numbered positions (second, fourth, sixth, etc.).
1+3+5+4+2=15 - Add the two results together.
57+15=72 -
Now what single digit number makes the total a multiple of 10? That’s the check digit.
72 plus 8 makes 80
4+2+4+5+3+1=19 19x3=57 1+3+5+4+2=15 57+15=72 and 8 makes 80. 8 is the check digit.
