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, 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 life at a British bookseller. In 1965, WHSmith announced a plan to label every book on its shelves with a numeric identifier 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 the purpose. David Whitaker in the UK and Emery Koltay at R. R. Bowker in the US each pushed the idea into their national publishing industries over the next two years, and 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 9-digit SBN was retired in the United Kingdom in 1974. Old SBN values can still be converted to ISBN-10 by prepending a leading zero, and the check digit carries over unchanged.

Thirty-seven years later the 10-digit namespace was straining. Worldwide book output had grown, self-publishing was about to explode, 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.

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. Understanding the layout makes the conversion process obvious, and it also explains why hyphen positions vary between systems.

ISBN-13 layout

Element	Length	What it identifies
Prefix element	3 digits	978 (historical "Bookland") or 979 (overflow since 2007, used in Italy, France, Korea, and the US)
Registration group	1 to 5 digits	Country, language area, or territory. Group 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.

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 just 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.

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 fresh namespace: GS1 allocates fresh registration groups inside it, independent of what existed under 978. As of this writing, 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 been on the 13-digit form since 2007, but ISBN-10 is still very much alive. These are the scenarios where a round-trip converter saves real time.

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, used by most large publishers and aggregators, allows either form in the ProductIdentifier element. Downstream systems may accept only one, which means ONIX producers often generate both values for each title. A converter is the cheapest way to keep them in sync without storing two columns of manually entered data.

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, which is an ISBN-10 to ISBN-13 round trip.

Academic citations and link rot

Older citation databases hold ISBN-10 values and link out to vendors that now expect ISBN-13 in their URLs. 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?

The International ISBN Agency expected the 10-digit namespace to run out as worldwide book output grew, and the publishing industry wanted ISBN to live inside the same retail barcode system as every other product. On 1 January 2007 the format moved to 13 digits, prefixed with 978 (the GS1 'Bookland' country code). Existing 10-digit values were migrated by prepending 978 and recomputing the check digit under the GS1 mod-10 rules. ISBN-13 is the same identifier as EAN-13 and GTIN-13, so a book and a can of beans can now be scanned by the same equipment at the same till.

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 numeric value 10. It is needed because ISBN-10 is a mod-11 calculation and eleven possible remainders need eleven symbols. The designers reused the roman numeral X so it would fit in a single character. When an ISBN-10 with X is converted to ISBN-13 under the mod-10 rules, the X disappears and is replaced by a regular 0 to 9 digit computed from the whole 13-digit payload.

Do the hyphens in an ISBN matter?

Semantically no. A computer reading an ISBN ignores the hyphens and works on the digit sequence. Visually and for display, the hyphens split the code into the prefix, registration group, registrant, publication, and check digit, which makes the meaning easier to read. Where the hyphens go depends on the real publisher range tables published by the International ISBN Agency and is not a fixed pattern, which is why two different systems can print the same ISBN with different hyphen positions. The converter here shows a best-effort display hyphenation and always preserves the canonical hyphen-free digit string so you can paste it anywhere.

Is every book guaranteed to have an ISBN?

No. ISBN is a voluntary commercial identifier run by the publishing industry. Self-published works, dissertations, internal reports, and many older books do not have one. Books published before 1970 rarely carry an ISBN because the standard did not exist yet; books published between 1968 and 1974 in the United Kingdom sometimes carry a 9-digit SBN, which is converted to ISBN-10 simply by prepending a leading zero without recomputing the check digit. Every edition and binding that is offered for sale commercially should have its own ISBN: the hardcover, the paperback, the ebook, and a large-print version each get a distinct number.

Is my pasted ISBN sent to a server?

No. The converter runs entirely in your browser. There is no API call, no logging, and no analytics payload carrying your input. You can paste internal or confidential catalogue data safely. Open your browser devtools network tab while you convert if you want to see for yourself: nothing fires.