The brain is the central control organ of the nervous system and arguably the most complex structure in the human body, governing thought, memory, emotion, coordination, and countless bodily functions. However, in terms of physical size and weight, the brain is not the largest organ. On average, an adult brain weighs about 3 pounds — far less than the skin, which can weigh over 8 pounds. While its role is critical for survival and function, the brain is smaller in both weight and surface area compared to the skin. It’s easy to overestimate the brain’s size because of its importance, but the skin actually takes up the most space and mass in the human body.