How do you know you're done having babies?

How do you know when, one, two, or even three babies are enough for you? If this baby is a girl I'm going to consider going ahead and getting my tubes tied, as Ill have a boy and a girl. but, in a way the thought of never being able to feel life move within me again breaks my heart a little. My husband only wants 2, and I know financially that's practical, but how do you know when enough is enough?