There are a grand total of two people I would consider to be friends, rather than just acquaintances.
Passing from the "acquaintance tier" to the "friend tier" doesn't take very long, though - it becomes abundantly clear to me almost immediately if people are going to be worthy of passing from one tier to the next. I suppose that sounds arrogant, but...well, I'm fed up with being fucked around with, stabbed in the back, abandoned, and all the rest of it. It's a lot easier and simpler if I keep people at arm's length unless I'm sure they're going to be worth the bother it'd take to form an emotional attachment to them. It'd take far too long to explain my thought processes and criterion for what separates friends from acquaintances and how one can become the other, so I won't even attempt but suffice it to say, it's entirely down to me, and time isn't a factor...nor is the amount of effort people might put into trying to befriend me.
But I suppose a friend, to me, is someone I am (almost) completely unguarded with; someone I can trust without any reservations. Someone who knows me as a person, rather than just a faceless figure who happens to share a few of their interests, or a convenient, non-judgemental listening ear for their worries and problems. Someone I am willing to let see who I am, rather than what I choose to show other people to keep them at bay.
I don't know how many people I talk to would see me as an actual friend. Two or three, perhaps? I don't really qualify as a friend for most people because I don't talk to them often enough and they know next to nothing about me as a person; people I talk to know what my interests are, but that's about all they know. But then, other people have far more relaxed standards for friendship than I do, so who knows? A lot of people I talk to ask me for advice or reveal things to me that I would never consider telling them in casual conversation if our positions were reversed, so it's hard for me to get a sense of it sometimes. Most people aren't as secretive as I am. It's not a question I really ask, because I never get a satisfactory answer...or an answer I can readily believe.