The Size of the Human Brain

Brain Weight, Brain Length, and Intelligence

woman looking at human statue with brain

Matt Cardy / Getty Images

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 it can do, you might wonder how big the brain is.

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

Compared to the size of our bodies, humans have much larger brains than many other mammals—but not the largest. The shrew's brain is about 10% of its body mass (for humans, it's about 2%).

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 human baby's brain weighs approximately 350 to 400 grams or three-quarters of a pound. The average brain is around 15 centimeters long.

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, 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.

Does Brain Size Matter?

Humans do not all 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 that 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 one analysis by Michael McDaniel of 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 we define and measure intelligence, whether we should account for relative body size when making such correlations, and which parts of the brain we should look at when making determinations about intelligence.

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

Frequently Asked Questions

  • How big is the human brain in inches?

    On average, the human brain measures about 5.5 x 6.5 x 3.6 inches (140 x 167 x 93 mm). It weighs about 3 pounds (1.3 kg).

  • At what age is the brain at full size?

    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.

3 Sources
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 numbersFront Neuroanat. 2014;8. doi:10.3389/fnana.2014.00046

  2. Herculano-Houzel S. The human brain in numbers: a linearly scaled-up primate brainFront 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

By Kendra Cherry, MSEd
Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."