→ The population size is measured by its density.
→ At given time, the organisms in the population is counted per given unit area.
→ For this the unit of measurement is decided such as unit per acre or unit per hectares. For small organisms, small units are considered.
→ In our country, every 10 years population is measured.
→ In a specific habitat, the population density is fluctuating. For instance in rainy season density is high whereas in dry season it is less.
→ The population density depends on the necessity of an organism.