Short answer
1230 grams. This is less than average. And from a big study, we know that brain size only explains very little of how smart a person is. The structure of the brain probably has a much larger effect on IQ than brain size.
Longer answer
We know that intelligence comes from the brain. Therefore, many people have thought that a bigger brain means higher intelligence. However, researchers of the McMaster University found that the brain of Einstein weighed only 1230 grams. In the graph below, you can see that for a man of age 76 (Einstein’s age when he passed away), this is relatively low! Instead, the researchers linked Einstein’s exceptional intellect to his parietal lobes, a brain region important for mathematical, visual, and spatial cognition. Einstein’s parietal lobes were 15% wider than the average parietal lobes. Was the low weight of Einstein’s brain an interesting exception, or does a person’s brain size say nothing about their intelligence?
IQ and brain size
In 2015, a big meta-analysis was performed to provide an answer to this question (Pietschnig, Penke, Wicherts, Zeiler, & Voracek, 2015). This means that the researchers combined the results of 88 different studies with in total over 8000 individuals that provided data on both brain size and intelligence, and compared them. They found a significant positive association of brain volume and IQ, meaning: the bigger a person’s brain, the higher their intelligence. However, the association that was found in this analysis was very weak: brain volume could only explain about 6% of the variation in IQ. This means that, although we could make an estimation about somebody’s IQ based on their brain size, this estimation will be wrong in a lot of cases, because most of the variation in intelligence results from other factors. According to Jakob Pietschnig, one of the researchers who did the meta-analysis, brain structure appears to be more important for IQ than brain size (“Larger brains do not lead to high IQs, new meta-analysis finds.,” 2015).
Conclusion and more..
The size of a person’s brain only explains a little bit of how smart that person is. The structure of the brain is probably more important for IQ. In the case of Einstein, the width of his parietal lobes might have contributed to his high intelligence. However, according to the scientific literature, there are many other brain regions and other factors associated with intelligence. And to make it even more complex, it seems to differ per person how much each factor contributes to their IQ level. So, we need to discover much more about the brain before we can say something about a person’s intelligence by simply looking at their brain.
Read more?
Larger brains do not lead to high IQs, new meta-analysis finds. (2015)
Pietschnig, J., Penke, L., Wicherts, J. M., Zeiler, M., & Voracek, M. (2015). Meta-analysis of associations between human brain volume and intelligence differences: How strong are they and what do they mean? Neuroscience & Biobehavioral Reviews, 57, 411-432.
Witelson, S. F., Kigar, D. L., & Harvey, T. (1999). The exceptional brain of Albert Einstein. Lancet, 353(9170), 2149-2153.