alex21:
I wonder what is the biggest t-shirt size? I saw 12XL or 15XL.
It varies greatly depending on country / region.
At one point in Australian sizes I was wearing 7XL shirts, which was the absolute largest I could (occasionally!) find in normal stores. After I got too big for them I bit the bullet and ordered some 9XL shirts from America. When they finally arrived I got a hell of a surprise with how large they were. I looked like a skinny person wearing one of my fat shirts 😅
When I actually measured myself and checked the size chart, in American sizes I was only a 4XL.
Being that OP is from Bulgaria, I suspect there's a very significant difference between a European 15XL and an American 15XL. I imagine you could use an American 15XL shirt as a car cover for a European hatchback 🤣