How Big Is a Human Brain? Learn About Brain Size and Brain Weight

Key Takeaways

• The average adult human brain weighs about 3 pounds and is fully formed by age 25.
• Men tend to have larger brains than women, but size doesn’t always mean more intelligence.

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.

Compared to the size of our bodies, humans have much larger brains than many other mammals—but not the largest. The brain makes up 2% of a human’s body mass, while the shrew’s brain is about 10% of its body mass.

In terms of sheer size, sperm whales and elephants take the top spots for weight at 18 and 11 pounds, respectively. But since even small elephants weigh 6,000 pounds or more, their brains are just 0.2% of their body weight. For the sperm whale, the brain is only about 0.06% of body weight.

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.

Researchers have found brain size can be linked to certain diseases or developmental conditions.

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.

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

1. Herculano-Houzel S, Avelino-de-Souza K, Neves K, et al. The elephant brain in numbers. Front Neuroanat. 2014;8. doi:10.3389/fnana.2014.00046

2. Herculano-Houzel S. The human brain in numbers: a linearly scaled-up primate brain. Front Hum Neurosci. 2009;3:31. doi:10.3389/neuro.09.031.2009

3. McDaniel M. Big-brained people are smarter: A meta-analysis of the relationship between in vivo brain volume and intelligence. Intelligence. 2005;33(4):337-346. doi:10.1016/j.intell.2004.11.005

Additional Reading

• Hoag H. Sex on the brain. New Scientist. 2008;199(2665):28-31.

• Park A. Brain size, early growth: clues to autism’s causes. Time. May 3, 2011.

• Park A. Bigger brains and higher IQ linked with specific genetic variants. Time. April 16, 2012.

• Schoenemann PT. Brain size scaling and body composition in mammals. Brain Behav Evol. 2004;63:47–60. doi:10.1159/000073759

By Kendra Cherry, MSEd

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the “Everything Psychology Book.”

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