ISBN Converter

Paste any ISBN-10 or ISBN-13 and get the other form with a recomputed check digit. Handles X check characters, 978 and 979 prefixes, and shows you why 979-prefixed values cannot convert back to the 10-digit form.

By The eancheck teamPublished Apr 11, 2026Updated Oct 9, 2026

Paste an ISBN to convert

Accepts ISBN-10 or ISBN-13, with or without hyphens or spaces. X check digits are preserved.

A short history of the ISBN

The ISBN began at a British bookseller. In 1965 WHSmith announced a plan to give every book on its shelves a number that a computer could process. In 1966 Gordon Foster, emeritus professor of statistics at Trinity College Dublin, devised a 9-digit Standard Book Number for it. David Whitaker in the UK and Emery Koltay at R. R. Bowker in the US took the idea to their national publishing industries over the next two years.

By 1970 the International Organization for Standardization had adopted the 10-digit form under ISO 2108, with the International ISBN Agency as the global registration authority. The United Kingdom retired the 9-digit SBN in 1974. An old SBN still converts to ISBN-10: put a 0 in front and keep the check digit.

Thirty-seven years later the 10-digit numbers were running short. Worldwide book output had grown, and the publishing industry wanted a single identifier that fitted the GTIN barcodes used by every other retail product. The fix was to move ISBN into the GS1 retail numbering system. On 1 January 2007 the format grew to 13 digits, with a three-digit prefix (978, and later 979) drawn from GS1's reserved "Bookland" namespace. Every existing ISBN-10 was migrated by prepending 978 to its nine-digit payload and recomputing the check digit under the GS1 mod-10 rules. That is the same operation this tool performs when you paste an ISBN-10.

To print the result as a book barcode, with a price add-on if you need one, use the EAN-13 barcode generator.

How an ISBN is assembled

An ISBN is not a random number. It is a structured identifier built from five parts in the 13-digit form and four parts in the 10-digit form. The layout shows what a conversion changes, and why hyphen positions vary between systems.

ISBN-13 layout

Element	Length	What it identifies
Prefix element	3 digits	978 (historical "Bookland") or 979 (added later for overflow, used in France, Italy, Korea and the US)
Registration group	1 to 5 digits	Country, language area, or territory. Groups 0 and 1 are English-speaking, 2 is French, 3 is German, 4 is Japan, 5 is Russian-speaking, 7 is mainland China.
Registrant element	Variable	The publisher. Allocated by the national ISBN agency. Larger publishers get shorter registrant blocks so they can issue more books per block.
Publication element	Variable	The specific edition or binding. Each hardcover, paperback, and ebook release gets its own publication element.
Check digit	1 digit	Computed by the GS1 mod-10 algorithm, always 0 to 9.

ISBN-10 layout

The 10-digit form omits the prefix element and runs straight from the registration group through to the check digit. The check character uses mod-11 instead of mod-10, which is why it can be an X when the remainder is 10.

The check digit math in both directions

Both algorithms are short enough to work out by hand if you want to verify what the tool is doing. They differ in the modulus they use and in how each position is weighted. To check a whole list of ISBN-13 values against the mod-10 rule at once, paste it into the check digit calculator.

ISBN-10, mod-11 with descending weights

Multiply each of the nine payload digits by the weights 10, 9, 8, 7, 6, 5, 4, 3, 2 from left to right. Sum the products. Take the remainder modulo 11. Subtract from 11 and take the remainder modulo 11 again. If the result is 10, write it as the letter X. Otherwise write the digit.

Worked example for the payload 030640615, which is the classic ISBN-10 0-306-40615-2.

0 times 10 is 0
3 times 9 is 27
0 times 8 is 0
6 times 7 is 42
4 times 6 is 24
0 times 5 is 0
6 times 4 is 24
1 times 3 is 3
5 times 2 is 10
Sum is 130. 130 mod 11 is 9. 11 minus 9 is 2.

The check character is 2, which matches the real ISBN-10.

ISBN-13, GS1 mod-10 with alternating weights

Multiply each of the twelve payload digits by an alternating weight of 1 and 3 from left to right, starting with 1. Sum the products. Take the remainder modulo 10. Subtract from 10 and take the remainder modulo 10 again. The result is always a single digit 0 to 9.

Worked example for the payload 978030640615, the 13-digit equivalent of the same book.

9 times 1, plus 7 times 3, plus 8 times 1, plus 0 times 3
plus 3 times 1, plus 0 times 3, plus 6 times 1, plus 4 times 3
plus 0 times 1, plus 6 times 3, plus 1 times 1, plus 5 times 3
Sum is 93. 93 mod 10 is 3. 10 minus 3 is 7.

The check digit is 7, giving 978-0-306-40615-7. Notice that the trailing character changed from 2 to 7 even though the book, the publisher, and the nine-digit body are the same. That is why you cannot paste the old check digit onto the new form.

When conversion works, and when it does not

From ISBN-10 to ISBN-13

Always possible. Drop the old check character, prepend 978, and run the GS1 mod-10 algorithm over the resulting twelve-digit payload to produce the new check digit. Every valid ISBN-10 has exactly one corresponding ISBN-13, and that is the number to print as the EAN-13 book barcode.

From ISBN-13 to ISBN-10

Only possible when the ISBN-13 begins with 978. Strip the three-digit prefix, drop the mod-10 check digit, and run the ISBN-10 mod-11 algorithm on the remaining nine digits. What comes out is exactly the ISBN-10 that existed before the 2007 transition, or a synthetic ISBN-10 that would have been valid if that publisher had registered with the old system.

Why 979-prefixed ISBN-13 cannot be converted

The 979 prefix was added to absorb overflow as 978 filled up. It is a separate namespace: the International ISBN Agency allocates registration groups inside it, independent of what existed under 978. 979-0 is reserved for ISMN (the International Standard Music Number for sheet music), 979-8 is the United States of America, 979-10 is France, 979-11 is Korea, and 979-12 is Italy. None of these groups has a counterpart in the old 10-digit ISBN namespace, so there is no 10-digit value to derive. The converter detects 979 inputs and tells you this directly instead of pretending.

Who needs an ISBN converter

Most software has used the 13-digit form since 2007, but ISBN-10 still turns up in old catalogues, citations and on back covers. These are the places where it has to be converted.

Library systems and MARC records

Library catalogues built on the MARC standard store book identifiers in field 020 and often hold both forms for the same book. Migrating a pre-2007 catalogue to a modern discovery layer means converting every ISBN-10 to ISBN-13 as part of the data normalisation step. The reverse conversion is also useful: when exchanging records with a legacy partner, you sometimes need to hand them the 10-digit form they expect.

ONIX feeds and metadata exchanges

The ONIX for Books XML format, which publishers and aggregators use to exchange title data, allows either form in the ProductIdentifier element. Downstream systems may accept only one, which means ONIX producers often generate both values for each title. Computing one from the other keeps them in step, with no second column typed by hand.

Used-book marketplaces

Sellers uploading stock listings often paste whatever they find on the back cover of the book, which might be a 10-digit value from 1995 or a 13-digit value from 2015. Marketplaces that index their inventory on ISBN-13 only need to convert incoming 10-digit values on the way in, a one-way ISBN-10 to ISBN-13 conversion. Magazines mixed into the stock carry an 8-character ISSN instead, which the barcode identifier recognises. When a digit on a worn cover cannot be read, the barcode repair tool finds the ISBN-13 values that fit the check digit.

Academic citations and link rot

Older citation databases hold ISBN-10 values and link out to vendors whose URLs expect ISBN-13. Converting at render time is cheaper than migrating the historical data, especially when the database is read-only.

Publisher reprints and back-catalogue work

When a publisher reprints a backlist title under a new binding, the book gets a new ISBN. But the original ISBN-10 is still in circulation in reference works, second-hand listings, and library holdings, so catalogue systems usually store both and can cross-reference one to the other.

Frequently asked questions

Why did ISBN change from 10 to 13 digits in 2007?

For two reasons. The International ISBN Agency expected the 10-digit numbers to run out as book output grew, and the book trade wanted ISBN inside the same retail barcode system as other products. On 1 January 2007 the format moved to 13 digits with the GS1 'Bookland' prefix 978. Each ISBN-10 became an ISBN-13 by adding 978 in front and recomputing the check digit under GS1 mod-10. An ISBN-13 is a valid EAN-13, so a book scans at the same till as a can of beans.

Can every ISBN-13 be converted to ISBN-10?

No. Only ISBN-13 values that begin with 978 can. The 979 prefix was added later for overflow, and the registration groups inside 979 (such as 979-8 for the United States or 979-10 for France) were never allocated in the old 10-digit namespace. There is nothing to convert back to. The converter detects 979 inputs and explains this instead of generating a fake value.

Why does the check digit change when I convert?

ISBN-10 and ISBN-13 use different check digit algorithms. ISBN-10 uses a mod-11 calculation with weights 10 down to 2 and a check character that can be 0 to 9 or the letter X (representing the value 10). ISBN-13 uses the GS1 mod-10 algorithm that every EAN-13 and GTIN-13 uses, with alternating weights of 1 and 3 and a check digit that is always 0 to 9. The payload digits are the same in both forms, but the trailing character is recomputed under whichever algorithm the target form uses.

What is the X in some ISBN-10 values?

The X is a check character that stands for the value 10. ISBN-10 uses a mod-11 calculation, and eleven possible remainders need eleven symbols, so 10 is written as X. When an ISBN-10 with X is converted to ISBN-13 under the mod-10 rules, the X disappears and is replaced by an ordinary digit from 0 to 9, computed from the whole 13-digit payload.

Do the hyphens in an ISBN matter?

Not to software. A computer reading an ISBN ignores the hyphens and works on the digits. For people, the hyphens split the number into prefix, registration group, registrant, publication and check digit. Where they go depends on range tables published by the International ISBN Agency, not on a fixed pattern, so two systems can hyphenate the same ISBN differently. The converter shows a best-effort hyphenation and always gives the plain digit string to paste.

Is every book guaranteed to have an ISBN?

No. ISBN is voluntary, and self-published works, dissertations, internal reports and many older books have none. Books from before 1970 rarely carry one, because the standard did not exist yet. UK books from 1968 to 1974 may carry a 9-digit SBN: put a 0 in front to get the ISBN-10 and keep the check digit. Every edition offered for sale should have its own ISBN, so the hardcover, paperback, ebook and large-print version each get a different number.

Is my pasted ISBN sent to a server?

No. The conversion runs in your browser, so an ISBN for a title that has not been announced yet, or a column copied from an unreleased catalogue, stays on your machine. Nothing is sent when you paste or convert; the result only leaves the page when you copy it.

Is the ISBN-13 the same number as the barcode on the back cover?

Yes. The 13 digits under the bars of a book barcode are the ISBN-13 without its hyphens, and the till reads them as an EAN-13. The five smaller digits to the right are a separate EAN-5 price add-on, not part of the ISBN. An older book may print its ISBN-10 above the bars, but no scanner reads that line. If only an ISBN-10 is printed, convert it before you make a new barcode.

How do I convert a whole column of ISBN-10s in Excel?

With a formula. Remove the hyphens and format the column as text, so a leading 0 is not lost. With the ISBN-10 in A2, use =978&LEFT(A2,9)&MOD(10-MOD(38+SUMPRODUCT(--MID(A2,{1,2,3,4,5,6,7,8,9},1),{3,1,3,1,3,1,3,1,3}),10),10). The 38 is the weighted sum of 978. The formula ignores the old check character, so a typo passes through: run a few rows through the converter, and paste the finished column into the check digit calculator.

Should a new book print both the ISBN-10 and the ISBN-13?

No. Since 1 January 2007 ISBNs are issued in the 13-digit form, and the Library of Congress asked publishers to supply only the ISBN-13 from 2007. A title with a 979 prefix has no ISBN-10 at all. A system that still wants 10 digits can derive them from a 978 ISBN-13, as the converter does, so print the ISBN-13 on the copyright page and under the barcode.