The average human brain weighs about 1360 grams, or 3 lbs. That’s about four times lighter than an elephant brain. The heaviest mammalian brain is found in the sperm whale – weighing 7711 grams (17 lbs). Larger brains are needed, in part, to control larger muscles. At the other end of the scale is the owl brain that weighs just over two grams. A bullfrog's brain is about one-tenth smaller than that.