Population size – it is the ACTUAL NUMBER OF INDIVIDUALS in a population.
Growth rate – it can be express in a percentage; year over year change; measure of economic growth from one period to another.
The population size is the absolute number of people in a given area. The growth rate is the change in that number of people over a set period of time.
For example the population size of your town could be 10000 people. The growth rate of your town from the year 2000 to 2005 is a calculation of the number of people added to your town and the number of people your town has lost over five years.
FACT: did you know that global birth rate is higher than the death rate?