This index tells us the number of persons living in urban areas for each person living in rural areas. It is calculated as follows:

According to the 1981 census of India, the urban population was 159,727,357, while the rural population was 525,457,335. Thus, for each rural Indian, there were 0.304 urban people in India in 1981.

When there are more urban than rural persons in a country the picture is quite different. For instance, in the United States in 1970, the urban population was 149,324,930, while the rural population was 53,886,996, indicating that, for each rural American, there were 2,771 urban Americans.

Though this index is also affected by the definition of what is urban, as in the case of the percentage of urban population, it has one advantage over it. For historical comparisons, it is a good measure, for it also indicates the tempo of urbanisation.