Population density measures the amount of people in a given area, generally per square kilometer or mile. It’s difficult to get a clear image of what these vast spaces actually represent, so I thought that it would be interesting to flip the equation on its head and figure out how much space there is on average per person. This “Personal Space” is very easy to calculate. In the imperial system, ft2 per person = 27,878,000/(people per mile2). In the metric system, m2 per person = 1,000,000/(people per km2).