I received an inquiry recently from a reader who acquired International Standard Book Numbers (ISBNs) a long time ago and wanted to know a few things:

1. Were the ISBNs still good? Could they be used?
2. How could he translate the old 10-digit ISBNs to the new 13-digit format?
3. Oh, also, he lost his ISBN logbook, so he needs to know if there’s a way to reconstruct the whole set.

Funny about that. I went through this exact same process a few years ago. My logbook was long gone, I had ISBNs that dated from the 1980s, the whole thing.

Here’s how I went about reconstructing the ISBNs and how you can too, if you’re in the same situation as my reader.

Now, there’s probably a really elegant solution to this problem. It might rely on the mathematics behind the computations that drive the ISBN.

But this article isn’t it. This is a pure trail-and-error hack, with one main virtue: it works.

Answering the Old ISBN Questions

I could assure my reader about his first question. ISBNs never wear out, expire, or go bad. You can use old ISBNs with no trouble.

The second question was easily solved with a utility from Bowker, the ISBN provider in the U.S.:

Official ISBN 10- to 13-Digit Converter

Now onto the tough part.

First, you need to understand how to read the ISBN to follow along. You can see this post for a complete description:

Self-Publishing Basics: How to Read an ISBN

Here’s a typical old-style, 10-digit ISBN:

0-936385-11-1

Suppose this was the only ISBN you had. With this one number you can figure out all the rest of the ISBNs in your block. Here’s how.

Look at that ISBN again. the “0-936385-” is never going to change. The “0” indicates a language group, and the “936385” is the publisher prefix. In this case it’s assigned to my publishing company, Marin Bookworks.

The “11” is simply a sequential number. With a 6-digit publisher prefix, like mine, you can have 100 unique ISBNs. So we know that the ISBNs just before and just after this one will look like this:

0-936385-09-?
0-936385-10-?
0-936385-11-1
0-936385-12-?
0-936385-13-?

See the pattern? So far, so good. We now have the basic structure and we could fill out all 100 spots, right? Except for those question marks.

In the sample, the “1” at the end of the 0-936385-11-1 is a check digit. It’s derived through a complex mathematical formula. That way it’s easy to tell if the ISBN is correctly written, or if a mistake was made in transcribing it.

So how are we going to find out those pesky check digits? Trial and error.

Let’s go back to the 10- to 13-digit converter. As it happens, if you put an incorrect code into the converter, it will reject it.

What this means is that all we have to do is put in the code up to the “?” and start trying digits one at a time until we don’t get the “Conversion failed. Please enter valid 10 or 13 digit ISBN” error message.

(This is the complete set of check digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and “X” for 10.)

I did this with the one of the ISBNs above. First I tried a check digit of “0” then “1” then “2” but each time I got the error message.

When I got to “3” the converter accepted it as a valid ISBN. Voila! At the same time, it gave me the 13-digit version. Here they are:

0-936385-10-3
978-0-936385-10-5

Notice that the check digits are different. You have to check each of the ISBNs through the converter to make sure you have the check digits right.

Now, I admit this is a crude method. Its one virtue is that it works. If you don’t have 100 or 1,000 ISBNs to reconstruct, it can save you a lot of time.

Perhaps readers know of an easier solution to this problem?