वहन क्षमता अथवा जनसंख्या वहन क्षमता किसी भौगोलिक क्षेत्र के पारितंत्र में किसी जीवधारी प्रजाति की उस अधिकतम जनसंख्या के रूप में परिभाषित की जाती है जिसे उस पारितंत्र के संसाधन पोषण प्रदान कर सकते हों। स्पष्ट है कि वहन क्षमता से अधिक जनसंख्या वृद्धि उस पारितंत्र पर दबाव डालेगी और अत्यधिक वृद्धि उस तंत्र के विफल होजाने का कारण भी बन सकती है।

The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as the environment's maximal load, which in population ecology corresponds to the population equilibrium, when the number of deaths in a population equals the number of births. The effect of carrying capacity on population dynamics is modelled with a logistic function. Carrying capacity is applied to the maximum population an environment can support in ecology, agriculture and fisheries. The term carrying capacity has been applied to a few different processes in the past before finally being applied to population limits in the 1950s. The notion of carrying capacity for humans is covered by the notion of sustainable population.