What size inlay would this have?

Hello all,

I am creating box set covers for every season of Doctor Who from 1963 because the range of classic series DVDs is coming to a close. I just thought it'd free up shelf space, and I'll happily share them on here when done.

I have found an ideal case to hold the seasons:

http://www.totalblankmedia.com/dvd-case-holds-10-discs-p-608.html

I can, however, find no information on the inlay size!

Any advice?