The expanding ranks of the middle class in the capital has grown to 5.4 million, some 40 percent of the city's permanent residents, according to a report released on July 17.

The study, which was published by the Social Science Academic Press and Beijing University of Technology, said the average income of a member of the middle class in Beijing is about 5,923 yuan per month. The total income of the average Beijing middle class family is 10,007 yuan per month.

According to a report from the World Bank in 2006, the middle class in developing countries should be defined as those people with a per capita income of $ 4,000 (about 27,100 yuan) or more. The average annual income of a member of the middle class in Beijing is 71,076 yuan, which is about 43,976 yuan more than the bottom line.