The average adult human brain weighs about 3 pounds (1300 to 1400 grams). A newborn human baby's brain weighs approximately 350 to 400 grams or three-quarters of a pound. The average brain is around 15 centimeters long. Neurons are the building blocks of the brain and nervous system. They transmit and carry information, allowing different parts of the brain to communicate. They also allow the brain to communicate with other parts of the body. Researchers currently estimate that there are around 86 billion neurons in the human brain.

Source: Very Well Mind