It just occurred to me when calling my college roommate that basically, it’s three. With my mom, I let it go all the way to voicemail, as she’s nearly 80 and may be on the other end of the house.
But with most of my friends, if they don’t answer in two rings, it’s a lost cause absent external influences.
5 to 6, I’m ringing a phone that’s more than likely on the person, so anything beyond 4 they are probably not gonna answer, I just give 5-6 I case their phones stuck in their pocket.