How heavy is a human brain?

Most references put the average adult brain at 1.2 to 1.4 kg (2.6 to 3.1 lb), about 2% of total body weight. Taking men and women together, the average is about 1.3 kg (2.9 lb). Men average about 1,370 g (some studies give 1,345 g) and women about 1,200 to 1,222 g, so the often quoted 1.4 kg is really the rounded figure for men alone.

Individual brains vary a lot. The standard reference range is 1,180 to 1,620 g (2.6 to 3.6 lb) for men and 1,030 to 1,400 g (2.3 to 3.1 lb) for women. In volume, that is around 1,260 cm³ for men and 1,130 cm³ for women. Men’s brains are heavier on average mainly because men are on average larger, and a large autopsy study found the overall gap to be 9.8%.

A newborn’s brain weighs about 360 g (girls) to 380 g (boys), roughly a quarter of its adult weight. Growth is fastest early on: by the end of the first year the brain has more than doubled, and by age 3 it is about four times its birth weight.

The best-known data on lifetime change come from Anatole Dekaban and Doris Sadowsky, who in 1978 picked 2,773 men and 1,963 women with healthy brains from more than 20,000 autopsy reports. Brain weight peaked at about age 19, began a slow decline at about 45 to 50, and by age 86 and over the average brain was about 11% lighter than at its peak. For a 1.3 kg brain, that is a loss of roughly 140 g.

Guinness World Records lists a brain of 2,850 g (6 lb 4.5 oz) as the heaviest ever measured, more than twice the usual weight. It belonged to a 21-year-old man with epilepsy and an intellectual disability who died at the Meerenberg asylum near Haarlem, and was weighed by the Dutch pathologist Gerard Christiaan van Walsem in 1899. Methods for removing and preserving brains were not standardized then, so the figure may be somewhat high.

A heavy brain is not the same as a brilliant one. Albert Einstein’s brain weighed 1,230 g (2.7 lb) when it was removed in 1955, below the average for men. Across many MRI studies, brain size and intelligence show only a moderate correlation of about 0.3 to 0.4.

Inside the skull the brain floats in cerebrospinal fluid. Its mass is still about 1.3 kg on average, but suspended in the fluid its net weight is equivalent to only 25 to 50 g (about 1 to 2 oz). Without that buoyancy, the soft tissue would press on its own lower parts hard enough to cut off their blood supply.

Light as it feels, the brain is expensive to run. At about 2% of body weight it receives about 15% of the blood pumped by the heart and uses about 20% of the body’s oxygen and 25% of its glucose. That demand barely changes between rest and hard thinking.