In 2013, a total of 706 U.S. students majoring in Chinese graduated, a gain of just 6 students over the previous year. In addition, Japanese as a major continues to attract significantly more students than Mandarin.
By way of contrast, in 2013 a total of 12,703 U.S. students graduated with degrees in Spanish.
Despite the strong growth of interest in Mandarin over the past two decades or so, only 2.34% of all students in U.S. universities majoring in a foreign language are majoring in Chinese, so the percentage of Mandarin majors among students overall is tiny indeed.
The numbers are for graduating seniors in those years.
Source: Data on Second Majors in Language and Literature, 2001–13, MLA Office of Research, Web publication, February 2015