ISSN Check Calculator
ISSN mod 11 check with spaced format.
What it does
ISSNs tag journals and serials the way ISBNs tag books: eight characters with a mod 11 check digit that catches typos before catalogs swallow them. Validators run the same weighted sum everywhere.
The tool above takes any ISSN as free text. It returns Valid or Invalid, the check digit note, and the spaced format.
The default 0378-5955 passes with check 5 from sum 160. The Nature classic 0028-0836 passes with 6, while ending 7 fails wanting 5.
The ISSN Centre defines the structure with MOD 11-2 arithmetic, and library ISSN services validate the same way for serials. X stands in where 10 lands.
Validation proves shape, never registration. Catalogs and publishers confirm titles and holdings, so treat Valid as ready to file, not proof of record.
How to use
- Type the ISSN.
- Read Valid or Invalid first.
- Read the check digit beside it.
- Copy the spaced format last.
- Recheck digits on failure.
- Confirm titles at registries.
Formula
- digits
- First 7 digits of the serial.
- weights
- Weights 8 down to 2.
- check
- 0-9 or X for 10.
ISSN International Centre defines the eight digit structure with MOD 11-2 check matching this weighting. Library of Congress ISSN services mirror the same validation for US serials. Check digits catch transpositions; only registries confirm titles.
Worked example
Example: validate a serial ISSN
Default: 0378-5955 example.
- Input: 0378-5955.
- Clean: 8 characters, last may be X.
- Weight: positions 8 down to 2.
- Sum: 0x8+3x7+7x6+8x5+5x4+9x3+5x2 = 160.
- Check: 160 mod 11 = 6, 11 minus 6 = 5.
- Tool shows Valid ISSN, Check 5 passes, 0378-5955.
Reference table
| Input | Math | Verdict |
|---|---|---|
| 0378-5955 | sum 160, want 5 | Valid |
| 0028-0836 | sum 82, want 6 | Valid |
| 0378-5957 | want 5, ends 7 | Invalid |
| 1234-5679 | sum 112, want 9 | Valid |
Limits
- Format check only.
- No title lookup.
- X handling per standard.
- Registry changes apart.
Common mistakes
- Typing O for 0.
- Dropping leading zeros.
- Trusting valid as registered.
- Confusing ISSN with ISBN.
- Pasting with hidden breaks.
Try it yourself
Quick checks. Answers sit tucked under each question.
0028-0836?
Valid ISSN, check 6 passes.
0378-5957?
Invalid ISSN: wants 5, ends 7.
12345?
Too short for any ISSN: enter 8 digits, last may be X.
Questions
Mod 11 how?
Weight first 7 digits 8 down to 2, mod 11, subtract from 11. Remainder 10 writes X.
ISSN or ISBN?
Serials and journals; books take ISBN. Same math family, different registries.
Valid means registered?
No. It proves the string is well formed, not that the title exists.
Explain failures?
Yes, when the string is well formed but the digit mismatches. The tool names the wanted digit.
X meaning?
The 8th digit: 0 to 9 or X standing for 10.
Spaces and lowercase?
Dashes and case do not matter; the tool strips and uppercases first.