Library of Congress


The Library of Congress > U.S. ISMN Agency > About the ISMN > Numerical Structure of ISMN
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ISMN are comprised of 13 digits divided into four elements and are printed as in this example:

13-digit ISMN printed on a barcode
  • Prefix element (always 979-0, denoting music)
  • Publisher element (variable in length; 2600, in this example)
  • Item element (variable in length; 0043, in this example)
  • Check digit (validating the number; 8, in this example)

Like the ISBN (International Standard Book Number), the ISMN is a “smart” number, containing a publisher identifier.  Unlike the ISBN, the ISMN contains no area/language prefix, as music is intrinsically international, suggesting no geographic/linguistic boundaries.

Prolific publishers receive an identifier of three or four digits; smaller publishers receive identifiers of five, six, or seven digits.

Check digit calculation:

The math for computing the check digit is based on a simple modulus 10, with alternating weights of 1 and 3 assigned from left to right.  Each of the first 12 digits (excluding the check digit itself) is multiplied by an alternating sequence of the numbers 1 and 3, from left to right.  The sum of the products thus obtained, plus the check digit, must be divisible, without remainder, by 10.   For example:

  prefix element publisher element item element check digit
ISBN 9  7   9  0 2   6   0   0 0   0   4   3 8
Weight 1  3   1  3 1   3   1   3 1   3   1   3  

Products 9+21+9+0 +2+18+0+0 +0+0+4+9 = 72

Total: 72 + 8 = 80  --> 8 = check digit

The U.S. ISMN Agency provides publishers with valid numbers, complete with appropriate check digits already calculated.

10-digit ISMN printed on a barcodePrior to January 1, 2008, ISMN consisted of ten digits, divided into four elements, and printed as in this example: 

These older ISMN are often encountered on earlier music publications and function just as the currently used 13-digit numbers.