calculating ISBN number

Calculating ISBN number

 

How do I calculate an ISBN-13 check digit?

 Like the UPC check digit, an ISBN-13 check digit is calculated like an EAN-13 symbol using a mod 10 calculation. The last digit in an ISBN13 barcode is a check digit based on the previous 12 numbers. Our example barcode data is "978123456789".

1.      Add the digits in the even-numbered positions (first, third, fifth, etc.) together.

        9+8+2+4+6+8=37

2.    Multiply that number by three.

        37x3 = 111

3.    Add the digits in the even-numbered positions (second, fourth, sixth, etc.) to the result.

        7+1+3+5+7+9=32

4.    Find the resulting modulo 10 (the number that when added will make the next multiple of 10).

        111+32=143 (the next multiple of 10 is 150)

        143+7 = 150

7 is the check digit.