Carrying capacity refers to the maximum population size of a biological species that can be sustained by a specific environment, given the food, habitat, water, and other resources available. It is the environments maximal load, which in population ecology corresponds to the population equilibrium, when the number of deaths in a population equals the number of births (as well as immigration and emigration) . The effect of carrying capacity on population dynamics is modeled with a logistic function. Carrying capacity is applied to the maximum population an environment can support in ecology, agriculture, and fisheries.

Carrying capacity is determined by environmental factors such as adequate food, shelter, water, and mates. If these needs are not met, the population will decrease until the resource rebounds. Limiting factors determine carrying capacity, and the availability of abiotic factors (such as water, oxygen, and space) and biotic factors (such as food) dictate how many organisms can live in an ecosystem. Carrying capacity is also impacted by the availability of decomposers, which break down and recycle dead organisms and organic matter.

A carrying capacity graph typically shows time vs. population size. Before the population reaches carrying capacity, it experiences exponential growth, which is not inhibited by limited resources. When the carrying capacity is reached, the population growth rate decreases, resulting in a leveled, relatively static population size.

In summary, carrying capacity is the maximum quantity of a specific population that an ecosystem can sustain based on the available resources.