Population size is the total number of individuals in a population, while population density is how many of those individuals are found per unit area or volume (how “crowded” they are).

Quick Scoop: Core Idea

  • Population size : Just the headcount of a species in a defined area (e.g., 1,000 rabbits in a forest).
  • Population density : Headcount per unit of space (e.g., 10 rabbits per square kilometer if those 1,000 rabbits live in 100 km²).

So, size asks “how many?”, density asks “how many per unit of space?”.

Mini Example Story

Imagine two islands:

  • Island A: 1,000 people on 1 square kilometer.
  • Island B: 1,000 people on 100 square kilometers.

Both have the same population size (1,000), but Island A has a much higher population density , meaning people are packed closely together, while Island B feels more spread out.

Why the Difference Matters

  • Population size helps show the overall scale of a population (risk of extinction, total resource needs, etc.).
  • Population density helps explain crowding, competition for resources, and how likely individuals are to interact, mate, or compete.

You can even calculate density using a simple relationship:
population density = population size ÷ area.

TL;DR:
Population size = total count of individuals.
Population density = number of individuals per unit area/volume (a measure of how crowded they are).

Information gathered from public forums or data available on the internet and portrayed here.