An ISBN looks like a random string of digits, and it is protected by a simple piece of arithmetic. The last digit of every ISBN is a check digit, calculated from the other digits by a fixed formula, so that a typing error, a transposed pair or a copy mistake can be caught. A number whose check digit does not agree with the rest is not a valid ISBN, and a retailer, a printer or a library system may reject it or, worse, match it to the wrong book.
Free tool · ISBN Validator Converter
ISBN Validator Converter that tells you whether an ISBN is valid and converts it for you
The isbn validator converter checks that an ISBN is valid by testing its check digit, converts between ISBN-10 and ISBN-13, and calculates the missing check digit if you enter the first nine or twelve digits, showing the ISBN-13 without hyphens and its ISBN-10 equivalent where one exists. It runs in your browser and is free for authors, publishers, librarians and booksellers.
Use the free tool
The isbn validator converter is free to use, with no account and nothing uploaded.
- Validate ISBN-10 and ISBN-13
- Convert both ways
- Missing digit calculated
Key facts
- FreeNo cost, no account and no usage limit on the isbn validator converter
- In your browserNothing that you type or paste into the isbn validator converter is uploaded
- SecondsTypical time from opening the isbn validator converter to a result
Free tool
ISBN validator and converter
Check that an ISBN is valid, convert between ISBN-10 and ISBN-13, or calculate a missing check digit.
The isbn validator and converter needs JavaScript, and it works in your browser without sending anything that you enter to a server.
Overview
What the isbn validator converter does and why it helps
The validator applies the formula. For an ISBN-13, it multiplies the first twelve digits alternately by 1 and 3, adds them, and finds the digit that brings the total to a multiple of ten. For an ISBN-10, it multiplies the first nine digits by 10, 9, 8 and so on down to 2, adds them and finds the digit, which can be an X for ten, that makes the total a multiple of eleven. Enter any ISBN, with or without hyphens, and the tool reports whether the check digit is correct, shows the ISBN-13 and the ISBN-10 equivalent and lets you complete a number if you only have the first twelve digits or the first nine.
Conversion matters because books published before 2007 carry ten-digit ISBNs, and modern systems use thirteen. An ISBN-10 becomes an ISBN-13 by adding 978 in front and recalculating the check digit, and the reverse is possible only for numbers that start with 978, since the 979 prefix has no ten-digit form. Use the tool before you enter an ISBN into a platform, a catalogue or a printed copyright page, to be sure that the number is both valid and the right one for the book in your hands.
The ISBN validator converter checks whether an ISBN is valid, converts between ISBN-10 and ISBN-13 and calculates missing check digits. This is a free isbn validator converter, built for authors who want a clear answer without buying software. Open the isbn validator converter online and it is ready at once, with no download. Use it as an isbn validator converter free online whenever you are mid-project. The wording and defaults suit an isbn validator converter for authors, not general business users. It also serves as an isbn validator converter for self-published books, whichever store you publish through. If you publish on Amazon, use it as an isbn validator converter for KDP too, since it follows that platform's rules. There is no account to create, so this isbn validator converter no sign up page is ready the moment it loads. This isbn validator converter tool for writers explains each step in plain words. If you are hunting for the best isbn validator converter, judge it by whether it explains its numbers, as this one does.
How to use it
How to use the isbn validator converter, step by step
Enter the ISBN
Type or paste the number with or without hyphens. The tool strips them before it checks anything. The isbn validator converter updates as you type, so you can correct a value and see the result straight away.
Read the validity result
The tool tests the check digit and tells you whether the ISBN is valid. A failure means a digit is wrong. Take your time with this step, because every later result in the isbn validator converter depends on it.
Convert between ISBN-10 and ISBN-13
The tool shows the other form where one exists. Not every ISBN-13 has an ISBN-10 equivalent. If a value looks wrong, change it and read the result again; the isbn validator converter never stores or uploads what you enter.
Calculate a missing check digit
Enter the first nine or twelve digits and the tool calculates the last digit for you. The isbn validator converter updates as you type, so you can correct a value and see the result straight away.
Compare with your records
Check that the ISBN matches the edition on your copyright page and in your accounts. Take your time with this step, because every later result in the isbn validator converter depends on it.
Copy the result
Copy the thirteen-digit form without hyphens for retailer systems. If a value looks wrong, change it and read the result again; the isbn validator converter never stores or uploads what you enter.
How the isbn validator converter works
A check digit that proves the number is consistent
Enter an ISBN with 10 or 13 digits, or the first 9 or 12 digits. The tool calculates the check digit by the rule for that length, compares it with the one that you gave and tells you whether the ISBN is valid. For ISBN-10, the check digit can be an X.
It also converts. An ISBN-10 becomes an ISBN-13 by adding the prefix 978 to its first nine digits and calculating a new check digit, and an ISBN-13 with the prefix 978 becomes an ISBN-10 by removing the prefix and calculating the ten-digit check. A 979 prefix has no ISBN-10 form.
A valid check digit shows that a number is internally consistent. It does not show that the number is assigned to your book, so check an ISBN against your registrar account, and keep a record of which ISBN belongs to which format and edition.
- Validation for both lengths
- Conversion in both directions
- Missing check digit calculated
Method
How the isbn validator converter works out its answer
ISBN-13 check
The first twelve digits are weighted 1, 3, 1, 3 and so on, summed, and the check digit is the amount that brings the sum up to the next multiple of ten.
ISBN-10 check
The first nine digits are weighted from 10 down to 2 and summed, and the check digit is the number that brings the total to a multiple of eleven, with X standing for ten.
Converting ten to thirteen
The tool puts 978 before the first nine digits of an ISBN-10, drops the old check digit and calculates a new one.
Converting thirteen to ten
For a 978 ISBN-13 the tool drops the prefix and the last digit and calculates the ten-digit check digit. A 979 number has no ISBN-10 equivalent.
Tips
Getting the most from the isbn validator converter
Copy and paste ISBNs
It avoids mistakes. The isbn validator converter is free and instant, so it is worth running again whenever your book changes.
Validate before you publish
A wrong number is expensive to fix. Make the isbn validator converter a routine step on every project, so that results stay consistent from book to book.
Keep a list of your ISBNs
Note the format and the title. A few minutes with the isbn validator converter now saves time across the whole manuscript.
Need it done for you?
When the isbn validator converter is not enough
The validator checks the number. These services use it correctly in your listings, your files and your cover.
ISBN Guidance
ISBN guidance covers how many ISBNs you need, which formats get which number and how to record them, so that every listing agrees.
See the service →Book Metadata Setup
Metadata setup enters your validated ISBN, title and categories on each platform without a single typing error.
See the service →Book Cover Barcode Placement
Barcode placement puts the barcode drawn from your ISBN on the back cover at the right size and position for your printer.
See the service →Before and after
Before and after using the isbn validator converter
The same publishing record, first with an ISBN typed from memory and then with a number that was checked and converted.
123Before
- 1An ISBN with a typo that nobody noticed
- 2A ten-digit number on a new listing
- 3An incomplete number missing its last digit
123After
- 1A number with a correct check digit
- 2An ISBN-13 on every listing
- 3A complete number calculated from its first digits
- 3problems found in the first review
- 3fixes checked in the final review
- 1named specialist owning every fix
- Fixedprice confirmed in the calculator before you order
No hidden typos
The check digit confirms that every digit is right before the number reaches print or a retailer.
The right format
The ISBN-13 is used everywhere, which modern platforms and libraries expect.
Complete numbers
Missing check digits are calculated, so the record is whole.
Client reviews
What authors say about our ISBN check service
Verified reviews from authors who asked a specialist to handle the ISBN check after using the isbn validator converter.
Getting historical fiction placed in the right categories on Amazon and IngramSpark required strategic metadata. The team understood the genre classification and the book reached the right readers from the first week.
My KDP file was rejected with a technical error message I could not understand. Book Formatting Experts diagnosed the problem immediately — a bleed issue on three pages — and corrected it the same day. Approved first time.
My YA novel needed to reach both English-language and Japanese readers. The multi-region distribution setup was handled correctly across all required platforms. International sales have exceeded my expectations.
The formatting error fix service saved my launch. My original formatter had made margin errors causing repeated rejection. Book Formatting Experts identified and fixed every issue within 48 hours. My launch was back on schedule.
My cookbook needed to be set up across multiple platforms simultaneously. The publishing support team handled every submission — KDP, IngramSpark, and Apple Books — with different requirements for each. Flawlessly executed.
The publishing readiness review identified four issues in my manuscript that would have caused rejection. Each was clearly explained and quickly resolved. My book launched without any technical complications.
Good publishing support overall. The KDP metadata setup was thorough. One category selection needed updating after initial launch but it was corrected promptly. The book is performing well in its target categories.
Good support throughout the KDP upload process. The metadata setup and category selection were explained clearly. One pricing setting needed adjustment after initial setup but it was corrected quickly.
Navigating IngramSpark's requirements for the first time felt overwhelming. The upload assistance handled everything — metadata, pricing setup, distribution channels. My children's book reached bookstores within two weeks.
As a first-time author, the technical side of self-publishing was genuinely daunting. The consultation covered every decision — platform choice, pricing strategy, metadata, and distribution. I launched with genuine confidence.
Excellent cover concept. One colour palette revision was needed — I wanted warmer tones — and the designer responded quickly with three alternatives. The final version is exactly right for my readership.
Academic EPUB with complex equations and references. One formula needed manual correction in revisions but the overall quality was exactly right. The file validates without errors on all platforms.
My cookbook had complex multi-column layouts and metric conversions. The formatting handled every element cleanly. One revision to tighten the index and it was exactly right. A professional result.
My self-help book needed a layout that felt warm and approachable without losing professionalism. The chapter openings, pull quotes, and action steps all worked visually together. Readers have commented on how easy it is to work through.
Fantasy books need careful layout to handle maps, epigraphs, and chapter artwork. Every element was handled with real understanding of the genre. The final interior is exactly what a fantasy reader expects.
My speaking and consulting enquiries increased noticeably after the website launched. The professional design and clear service pages communicate exactly what I offer. A worthwhile investment in my author business.
The cover communicates tension and danger without revealing too much of the plot. The design is original rather than using standard genre conventions. It stands out distinctively on Amazon search pages.
My EPUB was rejected twice by Apple Books before I found Book Formatting Experts. They identified the metadata errors, rebuilt the file properly, and the new version passed immediately. Wish I had contacted them first.
More free tools
More free tools to use with the isbn validator converter
Each of these tools is free, runs in your browser and works well alongside the isbn validator converter.
ISBN Hyphenation Tool
On this ISBN check job, free isbn hyphenation tool that works in your browser, plus a done-for-you ISBN formatting service.
Open the tool →ISBN Barcode Generator
Free isbn barcode generator that works in your browser, plus a done-for-you barcode and back cover service on this ISBN check project.
Open the tool →BISAC Code Finder
Free bisac code finder that works in your browser, plus a done-for-you BISAC code selection service for the ISBN check.
Open the tool →Universal Book Link Builder
For your ISBN check, free universal book link builder that works in your browser, plus a done-for-you buy link setup service.
Open the tool →QR Code Generator
For a ISBN check, free qr code generator that works in your browser, plus a done-for-you print layout service.
Open the tool →KDP Royalty Calculator
For your ISBN check, free kdp royalty calculator that works in your browser, plus a done-for-you KDP royalty review service.
Open the tool →FAQ
ISBN Validator Converter: questions answered
These are the questions authors ask most about the isbn validator converter, including accuracy, privacy and what to do next. If your question about the ISBN check is missing, request a quote and a specialist will reply.
What is an ISBN validator?
It is a tool that checks whether an ISBN is valid by testing its check digit with the standard formula.
How do I check if an ISBN is valid?
Enter it in the validator, and it tests the check digit for you. A number that fails has a typing error or is not a real ISBN.
How do I convert an ISBN-10 to an ISBN-13?
Put 978 in front of the first nine digits and calculate a new check digit. The tool does this for you.
Can every ISBN-13 be converted to an ISBN-10?
No. Only numbers that begin with 978 have a ten-digit form, and 979 numbers do not.
What is an ISBN check digit?
It is the last digit of the number, calculated from the others, so that a mistake in any digit can be detected.
How is the ISBN-13 check digit calculated?
Multiply the first twelve digits alternately by 1 and 3, add them up and take the amount needed to reach a multiple of ten.
What does X mean in an ISBN-10?
It stands for the value ten in the check digit position of an ISBN-10.
Can I calculate a missing check digit?
Yes. Enter the first nine or twelve digits and the tool gives the complete number.
Does a valid ISBN mean the book exists?
No. A valid ISBN has a correct check digit, but only the agency records show whether the number was assigned.
Do I need a new ISBN for each format?
Yes. The paperback, hardcover and ebook each need their own ISBN.
Does the isbn validator converter keep anything that I enter?
No. The isbn validator converter works in your browser, so what you enter stays on your device and is never saved.
Is the isbn validator converter free?
Yes, the validator costs nothing, needs no account and puts no limit on the numbers you check.
How does an isbn validator converter work?
It applies the check digit formula to see if the number is valid and recalculates when converting.
How to use an isbn validator converter?
Enter an ISBN and choose validate or convert.
Is there an isbn validator converter with examples?
Yes. The page includes a worked example so you can compare it with your own numbers or text. A sample ISBN is pre-filled.
Work with a specialist
Turn what you learn from the isbn validator converter into a finished book
The isbn validator converter costs nothing, and so does asking what a specialist would do with your book. When the isbn validator converter has done its part and you want finished files, a fixed price and one named person who owns the job, we are ready to start.