Yup, they run 2-3in bigger because they are measured C-C instead of the standard C-T.
That should be 2-3cm larger. There's a whole lot of info about this in the early pages of the Mercier Kilo TT Pictures thread. You could probably just read the first 10-20 pages (skip stuff you don't need right now at your own risk). Or you could just do a search.