How to calculate UPC-A check digits

To calculate a UPC-A check digit do the following:

1. Designate the right most of the 11 characters as odd.
2. Sum all of the characters in the odd positions and multiply the result by three.
3. Sum all of the characters in the even positions.
4. Add the even and odd totals from steps 2 and 3.
5. Figure out what the smallest number which, when added to the result from step 4, will result in a multiple of 10. This is the checksum character.

Example:

Number:   0 0 1 2 3 4 5 6 7 8 9
Position: O E O E O E O E O E O

Sum of odd positions:   0 + 1 + 3 + 5 + 7 + 9 = 25
Odd sum times three:    25 * 3 = 75

Sum of even Positions:  0 + 2 + 4 + 6 + 8 = 20
Sum of even and odd:    20 + 75 = 95

Smallest number to have a multiple of 10:  5

Checksum character = 5
UPC-A bar code =     001234567895

UPC-A checkdigits may also be calculated using a spreadsheet. Here is an Excel spreadsheet to download(self-extracting PKZip file) that will calculate UPC-A checkdigits.

Download UPC-A checkdigit spreadsheet