It can vary, if you mean how long is it in your blood it usually isnt very long. Only a few days to a week I believe. As far as piss goes, it can be anywhere from a week to a month, sometimes less and rarely more. It depends how much you smoke really. Someone who smokes once a month will probably be clean a week later at most. Someone who smokes a few times a day on a regular basis can take up to a month. Also things such as high water intake and exercise can help reduce the time.
thc is stored in the fat so the faster you work it out of the your system the less longer it'll be in there. do a search on it... theres tons about this question.