Ive worn a tank top, tee shirt, long sleeve shirt, jumper and jacket before! 5 layers! Though that was when I was in Melbourne on holiday. It doesn't get that cold living in WA, when it does I'll wear 3 layers.
Four - thermal long sleeved shirt, shirt, jumper and jacket with hood. That was only once when it was really cold though. Normally I would only wear two layers, shirt and jacket, as many places are over heated in winter and it would be too hot with a lot of layers on.
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.