Quick answer: about three weeks.
More involved answer: It really depends on the kind of beer, what gravity it is, how much and what kind of yeast you use, what temperature you're storing it at and other conditions. But, basically, assume about two weeks of conditioning around 65*-70* and another week in the fridge to clarify.
That said, I've had well carbed bottles after a week and I've had some that have taken nearly two months to get any decent kind of carbonation.