the number of persons per square kilometer in a country is called
Population density For humans, population density is the number of people per unit of area, usually quoted per square kilometer or square mile (which may include or exclude, for example, areas of water or glaciers). Commonly this may be calculated for a county, city, country, another territory or the entire world.
World population In demographics, the world population is the total number of humans currently living, and was estimated to have reached 7.6 billion people as of May 2018.[1]