Converting Between ISBN-10 and ISBN-13

David Kane asked the web4libbers:

Can anyone tell me what the conversion between ISBN-10 and ISBN-13 is, please. I need to write a little conversion program. Anything in PHP, for example.


“There is already an online converter:;” some pointing at Wikipedia on ISBNs, Bookland, and EANs; John Blyberg’s PHP port of the PERL ISBN-10/13 tool; some explanation that you have to watch the check digit, and discussion about why you’d need to do all this conversion.

Finally, Tim asked:

Someone should offer single and batch converstion as a free API, not an online form and an offer to have a “representive” call you for larger jobs.

Does anyone want that, or shall I?

And I answered: changed:

Same usage as xISBN and thingISBN. Returns empty result on invalid ISBNs.

Based on Blyberg’s code, incorporates some changes, may not be accurate. Poke at it, break it. Report findings, but don’t blame me if it returns incorrect results (I will try to fix the code/service, though).

Geeky extra: anybody know the Lat and Lon to Bookland? I’d really like to put this post on the map.