Calculating a CHECKSUM on a UPC will help you validate that it is, indeed, a valid Barcode.  To do this in EXCEL you can use this formula.  Just COPY+PASTE and REPLACE "B142" with the cell you are trying to validate


=IF(LEN(B142)<12,FALSE,TEXT(10-MOD(((MID(B142,1,1)+MID(B142,3,1)+MID(B142,5,1)+MID(B142,7,1)+MID(B142,9,1)+MID(B142,11,1))*3)+MID(B142,2,1)+MID(B142,4,1)+MID(B142,6,1)+MID(B142,8,1)+MID(B142,10,1),10),"0")=TEXT(RIGHT(B142,1),"0"))


Here is some more information about how the UPC check digit is calculated.

UPC

The final digit of a Universal Product Code is a check digit computed as follows:[2]

  1. Add the digits in the odd-numbered positions from the right (first, third, fifth, etc. - not including the check digit) together and multiply by three.
  2. Add the digits (up to but not including the check digit) in the even-numbered positions (second, fourth, sixth, etc.) to the result.
  3. Take the remainder of the result divided by 10 (ie. the modulo 10 operation). If the remainder is equal to 0 then use 0 as the check digit, and if not 0 subtract the remainder from 10 to derive the check digit.

For instance, the UPC-A barcode for a box of tissues is "036000241457". The last digit is the check digit "7", and if the other numbers are correct then the check digit calculation must produce 7.

  1. Add the odd number digits: 0+6+0+2+1+5 = 14.
  2. Multiply the result by 3: 14 × 3 = 42.
  3. Add the even number digits: 3+0+0+4+4 = 11.
  4. Add the two results together: 42 + 11 = 53.
  5. To calculate the check digit, take the remainder of (53 / 10), which is also known as (53 modulo 10), and if not 0, subtract from 10. Therefore, the check digit value is 7. i.e. (53 / 10) = 5 remainder 3; 10 - 3 = 7.