ISMN are comprised of 13 digits divided into four elements and are printed as in this example:
- 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.
Prior 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.
