Multiple choice general knowledge The average weight of an adult brain weighs? 3.5 pounds 3 pounds 2.5 pounds 4 pounds Reveal answer Fill a bubble to check yourself B Correct answer Explanation The average adult human brain weighs approximately 3 pounds (1.3-1.4 kg). This is a well-established anatomical fact. The brain accounts for about 2% of body weight despite consuming 20% of the body's oxygen.