Choose the unit of physical space that is to be used. Population density is a measurement of the number of people per unit area. That unit area can be small, such as a neighborhood, or large, such as a country or continent.
A common measurement used when speaking of population density is square mile. Either measure the physical area or locate the length and width from a reliable resource, such as a map.
Learn the population count present within the boundaries of the area. Depending on the size of the area, you might consult official census records to obtain the population count.
The population number is the numerator, and the area is the denominator. Divide the numerator by the denominator to obtain the population density. This figure frequently is expressed in terms of number of people per square mile, for example.