The Size of the Human Brain

The human brain is an amazing organ. It's capable of surprising feats of memory and learning. It's susceptible to damage, and yet remarkably adaptable to change. Considering all of its many capabilities, you may begin to wonder, how big is the human brain?

While the human brain has a structure similar to that of other mammals, what makes it different is it's size in relation to the rest of the human body.

Human Brain Size Stats

The average adult human brain weighs about 3 pounds (1300 to 1400 grams). A newborn baby's brain weighs approximately three-quarters of a pound (350 to 400 grams). On average, the human brain measures about 5.5 x 6.5 x 3.6 inches (140 x 167 x 93 mm).

The brain is considered fully formed at age 25. It develops from back to front, ending at the prefrontal cortex; this is the part of the brain that's responsible for decision-making and reasoning.

Men tend to have bigger brains than women. After taking overall body weight into account, men's brains tend to be approximately 100 grams larger than women's.

In women, parts of the frontal lobe and limbic cortex (areas associated with problem-solving and emotional regulation) tend to be bigger than those of men. In men, the parietal cortex (associated with the perception of space) and amygdala (involved in the processing of memory and emotional responses) tend to be larger than those in women.

Neurons are the building blocks of the brain and nervous system – they transmit and carry information, thus allowing different parts of the brain and body to communicate with one another. Researchers currently estimate that there are around 86 billion neurons in the human brain.

Does Brain Size Matter?

All humans do not have the same size brain. Does that mean that highly intelligent people have bigger brains? In some cases, there might be a link.

Autistic children tend to have bigger brains (and earlier disproportionate brain growth) than non-autistic children. The hippocampus (an area of the brain strongly associated with memory) tends to be smaller in older adults with Alzheimer's disease.

What about intelligence? It depends on who you ask. According to an analysis done by Dr. Michael McDaniel, a professor at Virginia Commonwealth University, many studies have found a correlation between bigger brains and higher intelligence.

However, not all researchers agree with McDaniel's conclusions. Such studies also raise important questions about how intelligence is defined and measured, whether relative body size is taken into account when making such correlations, and which parts of the brain should be looked at when evaluating intelligence.

It is also important to note that variations in brain size between humans are relatively small. Other influences that could play a pivotal role in determining intelligence include the density of neurons in the brain, social and cultural factors, and other structural differences inside the brain.