An adult human brain usually weighs between 1.2 kg and 1.4 kg. Individuals can have different brain weights due to factors like age and gender. Men’s brains often weigh about 1.37 kg, while women’s are closer to 1.20 kg on average. Yet, most scientific and educational discussions tend to use the standard estimate of 1.4 kg, which is about 3 pounds, as a reference point.