I'd say one if that, for a defensive bite.

BUT!

One time, one of my bigger ones nailed me. He got a hold of my pointer finger, and thought it was a rat lol. He held on for about 5 seconds trying to get a better grip, and let go. I'd give that a 2 lol. Didn't hurt, but definitely hurt more then a defensive nip. When they tag you, its like you don't even feel it. I usually bug out and jump like a baby, but laugh when its done. Its funny because you jump even though you know its not going to hurt