How to use the check digit validator (luhn, isbn, upc, ean)
- Choose the check digit scheme: Luhn, ISBN-10, ISBN-13, UPC-A, EAN-13 or EAN-8.
- Enter the number. Spaces and hyphens are ignored, and an ISBN-10 may end in X.
- Tick the box if your number is missing its last digit and you want the tool to calculate it.
- Read whether the check digit is valid and what it should be, with the method written out.
Formula
Luhn: from the digit next to the check digit, double every second digit (subtract 9 if over 9), add all digits, and the check digit makes the total a multiple of 10
ISBN-10: weights 10 down to 1 on all ten characters (X is 10), and the total must be a multiple of 11
ISBN-13, EAN-13, UPC-A and EAN-8: weights 3 and 1 alternating from the digit next to the check digit, and the total with the check digit must be a multiple of 10
Calculating the missing check digit means finding the one digit (or X for ISBN-10) that makes the total satisfy the rule.
A few well-known numbers
The Luhn example 79927398713 is valid, and changing the last digit to 0 makes it invalid because the check digit should be 3. The ISBN-10 0-306-40615-2 is valid, and 0-306-40615-3 is not. The ISBN-13 978-0-306-40615-7 is valid, and a final 8 is not.
The UPC 036000291452 is valid, the EAN-13 4006381333931 is valid and the EAN-8 96385074 is valid. Given 03600029145 without its check digit, the UPC-A check digit is 2, and 080442957 gets an ISBN-10 check character of X.
What a check digit is for
A check digit is one extra digit added to a number so that typing mistakes are easy to catch. It is worked out from the other digits, and if a digit is mistyped or two neighbors swap, the total usually no longer fits the rule. Luhn is used for many identification numbers, ISBN-10 and ISBN-13 for books, and UPC and EAN for retail barcodes.
The methods were checked against published example numbers and re-computed independently in code, but no outside source page was fetched for this tool, so use the written method above as the definition.
What a valid result does not mean
A matching check digit only means the digits are consistent with the scheme. It does not show that the number belongs to a real card, book or product, and it says nothing about whether an account exists or is active. Do not use it to verify identity or payment. Many random numbers pass by chance, about 1 in 10 for a single check digit.
The check also does not catch every mistake. Some errors, such as certain swaps, produce the same total. Nothing is sent anywhere, and the number you enter is processed in your browser. For barcodes, see the barcode generator, for number systems the number base converter, and for ID strings the UUID generator. The prime number calculator covers number theory.
Assumptions and limits
- The tool implements Luhn, ISBN-10, ISBN-13, UPC-A, EAN-13 and EAN-8 as written in the formula section.
- Only the check digit rule is tested. Length is checked for the fixed length schemes, and ISBN-13 numbers should begin with 978 or 979.
- A valid result never means the number is a real account, book or product.
- Spaces and hyphens are removed. Any other character is an error.
Frequently asked questions
What is the Luhn algorithm?
It is a simple checksum. Double every second digit from the right, add all the digits, and the total must be a multiple of 10. It catches most single digit typos and many swaps.
How do I validate an ISBN-10?
Multiply the ten characters by 10 down to 1, treating a final X as 10, and add them. The ISBN-10 is valid when the total is a multiple of 11.
Does a valid number mean it is a real card or product?
No. It only means the check digit fits the rule. The number may not belong to anything, so never use it to verify an account.
How is the UPC check digit worked out?
Multiply the first eleven digits by 3 and 1 in turn, starting with 3 on the first digit, add them, and choose the digit that brings the total to a multiple of 10.