According to the US Foreign Service Institute, an already bilingual native speaker of English with an adult vocabulary will need 2200 hours of class, so at least 88 weeks, to get fluent in Mandarin (or any other of the sinitic languages)
How long would it take me to learn Mandarin?
It depend on yourself. You can choose a good school, such as Mandarin Garden.
It depends on if you want to speak it fluently or just for some conversation using, so for speak it well you have to learn it for a few years but if you have the chance to speak it everyday then it might be for a year only.
