The largest organ of the human body is the skin. In an adult it covers 1.5 to 2 square meters, according to Germany's IQWiG. The largest organ inside the body is the liver. In an autopsy series of healthy young adults it averaged 1,561 g in men and 1,288 g in women. The longest organ is the small intestine, about 3.3 meters in living people.
The ten largest organs by weight
Two sets of figures sit side by side in the table. The first is a set of reference masses from the International Commission on Radiological Protection (ICRP). Its Publication 89 sets them for a 73 kg man and a 60 kg woman. The second set is measured. Molina and DiMaio weighed the organs of 232 men and 102 women aged 18 to 35 at the medical examiner's office in San Antonio, Texas. All had died suddenly of injuries and showed no disease.
| Organ | Reference man (g) | Reference woman (g) | Autopsy mean, men (g) | Autopsy mean, women (g) |
|---|---|---|---|---|
| Skin | 3,300 | not given | not weighed | not weighed |
| Liver | 1,800 | 1,400 | 1,561 | 1,288 |
| Brain | 1,450 | 1,300 | 1,407 | 1,233 |
| Lungs, both | 1,200 | 950 | 840 | 639 |
| Small intestine | 650 | 600 | not weighed | not weighed |
| Large intestine | 370 | 360 | not weighed | not weighed |
| Heart | 330 | 250 | 331 | 245 |
| Kidneys, both | 310 | 275 | 266 | 224 |
| Spleen | 150 | 130 | 139 | 115 |
| Stomach | 150 | 140 | not weighed | not weighed |
A few details affect the comparison. The reference lung mass includes the blood held in the lungs. The stomach and heart figures are wall tissue only, and the intestine figures leave out contents. The large intestine is the right colon, left colon and rectum added together.
The pancreas comes next, at 140 g in the reference man and 120 g in the reference woman. In the reference woman the breasts are set at 500 g for the pair, which places them between the small and the large intestine. Her two kidneys, at 275 g, also outweigh her heart at 250 g.
Skeletal muscle and the skeleton are left out of the list. Both are far heavier than any organ in it. Each is one of the organ systems of the human body, made of many separate muscles or bones.
How large the skin is, and why its weight differs between references
On area the references agree. Germany's Institute for Quality and Efficiency in Health Care (IQWiG) gives 1.5 to 2 square meters. The ICRP reference man has a body surface of 1.90 square meters.
On weight they do not. IQWiG says about one seventh of body weight, or 3.5 to 10 kg depending on height and body mass. The ICRP reference man has 3,300 g of skin, about 4.5 percent of his 73 kg.
The difference is the fat layer. IQWiG describes skin as three layers and includes the deepest one, the subcutis, which stores fat. A paper that uses the ICRP figure pairs it with a skin about 1.6 mm thick, counted as epidermis and dermis. Gray's Anatomy (1918) describes the skin itself as two layers, the corium and the epidermis.
The largest internal organ: the liver
MedlinePlus, the health site of the US National Library of Medicine, calls the liver the largest organ inside the body. The SEER module calls it the largest gland and places it just beneath the diaphragm, mainly on the right side of the abdomen. Gray's Anatomy gives its weight as 1.4 to 1.6 kg in men and 1.2 to 1.4 kg in women. The organ locator shows where the liver sits.
In the autopsy series the liver ranged from 838 to 2,584 g in men and from 775 to 2,395 g in women. The authors found that height, weight and body mass index could not predict organ weight. They proposed reference ranges instead: 968 to 1,860 g for a man's liver and 603 to 1,767 g for a woman's.
The longest organ: the small intestine
A review of measurements in living people puts the whole route from mouth to anus at about 5 meters, two thirds of it small intestine, or about 3.3 meters. Its three parts are the duodenum, the jejunum and the ileum. Gray's Anatomy gives the duodenum as about 25 cm.
Other references print longer figures. StatPearls gives an average adult length of 22 feet, or 7 meters. A French study of 200 cadavers measured the whole intestine, small and large together, at 795.5 cm on average, and found it longer in men. That is more than the 5 meters measured in living people.
Heaviest organs in men and in women
In the autopsy series the order of the organs was the same in both sexes: liver, brain, lungs, heart, kidneys, spleen. Each organ averaged heavier in the men, who were also larger on average: 173 cm and 76.4 kg, against 160 cm and 65.3 kg for the women.
The heart shows the size of the gap, with a mean of 331 g in men and 245 g in women. Gray's Anatomy gives similar figures: 280 to 340 g for a male heart and 230 to 280 g for a female heart.
Is skin really the largest organ?
The answer depends on what counts as an organ and on what is measured. SEER defines an organ as several kinds of tissue arranged so that together they perform a special function. MedlinePlus and StatPearls both name the skin as the largest organ.
Dermatology journals have carried the argument all the same. A 1990 editorial in Archives of Dermatology was titled "My organ is bigger than your organ". A 2014 letter in the Journal of Investigative Dermatology was titled "Skin is not the largest organ".
By weight, skeletal muscle is 29 kg in the ICRP reference man and the skeleton is 10.5 kg, against 3,300 g of skin. SEER lists each as a major system, and the skeleton alone has 206 bones in an adult.
By surface, a 2017 paper in the Journal of Investigative Dermatology cites the accepted values. They are 2 square meters for the skin, 30 for the lining of the gut and 50 for the lungs. Its author argues that hair follicles and glands raise the skin's own lining to at least 30 square meters.
New candidates have been put forward too. A 2016 review in The Lancet Gastroenterology and Hepatology argued that the mesentery should be classed as an organ. The mesentery is the tissue that tethers the small intestine to the back wall of the abdomen.
In 2018 a paper in Scientific Reports described fluid-filled spaces in connective tissue across the body. The spaces lie in the dermis of the skin and the walls of the digestive tract, among other places. HealthDay reported that its authors saw this interstitium as an organ in its own right and one of the largest in the body. The paper itself describes a space within and between tissues and does not use the word organ for it. One author said the label was unofficial until other researchers agree, in a report carried by Scientific American.