Just a clarification on Gareth Rees answer that I found to be very helpful. I downloaded the Full Range XML and found that the publisher ranges were not formatted the same as in his example. That made it a little difficult to determine how to find which group to use, so I found that if you take the next 7 digits after the prefix (all publisher group ranges are formatted as 7 digits numbers), they fall into one of the publisher groups and then you can get the length. It worked for several books on my shelf. Hopefully this will help others that were wondering specifically how to find the range.