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ISSN Validator

Check whether a serial's ISSN is valid.

How it is calculated

An ISSN has eight characters: seven digits and a check character. The tool removes spaces and hyphens, then multiplies the first seven digits by the weights 8, 7, 6, 5, 4, 3, 2 and adds them up. The check digit is (11 − (sum mod 11)) mod 11; a result of 10 is written as the letter X. The ISSN is valid when the eighth character equals this computed value.

The input must be exactly seven digits followed by a digit or X (lowercase x is accepted); anything else gives no result. The tool also shows the check character it computed, so for a mistyped number you can see what the last character should have been. It only checks the arithmetic, not whether the ISSN is actually assigned to a publication.

Worked example

Check 0317-8471. Weighted products: 0×8 = 0, 3×7 = 21, 1×6 = 6, 7×5 = 35, 8×4 = 32, 4×3 = 12, 7×2 = 14. The sum is 120. 120 mod 11 = 10, so the check digit is 11 − 10 = 1. The last character of the ISSN is 1, so the status is Valid.

Try this example →

Common mistakes

  • Confusing an ISSN with an ISBN. ISBN-13 uses a different check method; an 8-digit serial number goes here, a book number does not.
  • Entering the ISSN without its last character, or with the hyphen in the wrong place. Seven digits with no check character gives no result.
  • Reading an X as a mistake. X stands for a check value of 10 and is perfectly valid in the last position only.
  • Assuming a valid result means the journal exists. A passing checksum only proves the digits are self-consistent.

About this calculator

This tool checks whether an 8-digit ISSN (International Standard Serial Number) is valid by recalculating its check digit using a mod-11 weighted checksum: each of the first seven digits is multiplied by a descending weight from 8 to 2, the products are summed, and 11 minus the remainder (mod 11) gives the check digit — where a remainder of 1 corresponds to the letter 'X'.

Librarians, publishers, and researchers cataloging journals, magazines, and other periodicals use it to catch a mistyped or misprinted ISSN before citing a source or entering it into a library system. Enter the 8-character ISSN (with or without the hyphen) to check its check digit.

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