I am already wearing 3 or 4 and it is not even winter -being thin, I think I feel the cold more than people with a bit more fat on them.
The most I have ever worn was when I took my children to Disneyland in France and the temperature was about minus 15 and there were still queues to get into everything!
I think i had about 5 layers on and still could not feel my feet after a while.