The PW is 4.6" x 6.7".
The K4 (non-touch) is 4.5" x 6.5".
The K Touch is 4.7" x 6.8".
Generation 4 could be the K4 non-touch screen or the Touch model depending on what the advertiser means by Gen 4.
I have a non-Amazon, generic cover by Belkin that worked well with my Touch and now works well with my PW. But the Touch is slightly bigger than the PW. A cover designed for the smaller K4 non-touch might be too small.