The Physics
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Mass of a Human Brain

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Bibliographic Entry Result
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Nelson, Gideon E. Fundamental Concepts of Biology. New York: Wiley, 1982: 262.
AnimalBrain sizeRatio of brain size to body mass
human1500 g1/50
1,500 g
"Brain." Grolier Multimedia Encyclopedia. CD-ROM. 1995. "The average human brain at weighs 390g (14oz); its average maximum weight, reached at age 15, is 1315g (46oz)." 1,315 g
396 g
Brain Size, Body Weight and Intelligence. The High North Alliance brochure; "Living off the Sea, Minke Whaling in the North East Atlantic", February 1994. [see table below] 1,500 g
Chudler, Eric H. Brain Facts and Figures. University of Washington.
SpeciesWeight (g)
adult human1300-1400
newborn human350- 400
1,300-1,400 g
350-400 g
An Introduction to the Brain. A Relationship Between Evolution, Genetics, Morality, Ethics, Psychology, Education, and Culture. "The size of the modern human adult brain is about 1350 cc." 1,350 g

The mass of a newborn human brain is about 350-400g. The mass of an adult human brain is about 1,300 to 1,400 g. The brain makes up about two percent of the human"s mass. Its average width is about 140 mm, average length is about 167 mm, and average height about 93 mm.

According to the Grolier Multimedia Encyclopedia, "A theory has been proposed which states that behavioral capacity, a broad term indicating intelligence, is related not to the size of the brain but to the index of cephalization -- the amount of brain in excess of that required for transmitting to and from the brain." Another source (High North Alliance) states "neither absolute brain weight nor the relationship between brain weight and body size provide us with sensible criteria for comparing the intelligence of different species". Therefore meaning, the size of the brain doesn't necessarily determine the intelligence of that species. The table below shows this; because we know that humans are more intelligent than the other species on the chart, yet our brains are considerably smaller than most.

Species          Brain weight   Body weight   Brain weight
                   (gram)        (tonne)   as % of body weight
Man                 1500           0,07           2,1
Bottlenose dolphin  1600           0,17           0,94
Dolphin              840           0,11           0,74
Asian elephant      7500           5,0            0,15
Killer whale        5620           6,0            0,094
Cow                  500           0,5            0,1
Pilot whale         2670           3,5            0,076
Sperm whale         7820           37,0           0,021
Fin whale           6930           90,0           0,008
Mouse                0,4           0,000,012      3,2
Source: High North Alliance

Rachel Scott- Rosenbluth -- 2003