Biotic potential and environmental resistance determine the carrying capacity.
The maximum capacity of reproduction of a species under adequate environmental conditions is known as biotic potential. On the other hand, environmental resistance is a factor or things that restrict the growth of a population. These comprise disease, predators, lack of food, and competition.
These both determine the carrying capacity of a species. It is the maximum size of the population of the species, which the environment can maintain indefinitely, provided the habitat, food, and other important components accessible in the surroundings.