Endometrium Thickness is 4mm… good or bad?

Hi ladies! Sorry if this is may be a dumb question. Anyone have any knowledge about endometrium thickness? When I had my IUD removed, they did a ultrasound to make sure it was in place still and on my ultrasound results I noticed they measured my endometrium thickness which was 4mm and my ovaries. My left ovary is slighty bigger than the right. Which is interesting because I feel most of my cramping on my left. Is 4mm low? Or could that have something to do with my IUD and not having any periods at the time?

TIA💕