An article on BBC News reports that according the the Chinese Ministry of Education, some 30% of the people in China don’t speak Mandarin, of the 70% who do speak it, “many do not do it well enough”. As a result the Chinese government has apparently “launched another push for linguistic unity in China”. They will be promoting Mandarin particularly in rural areas and among ethnic minorities. A move that might not be welcomed by all.
China’s current population is 1,359,830,000 [source], so there are some 407,949,000 people in China who do not speak Mandarin, and around 951,881,000 who do – a very large number of people, though not as many as is generally believed. The idea that over a billion people speak Chinese is true if you count all varieties of Chinese, but not for Mandarin.