Most internal organs are surprisingly light. Your brain weighs roughly 1,300 grams (about 3 pounds), your liver comes in around 1,300 to 1,500 grams, and your heart sits at roughly 270 to 310 grams, or about the weight of a can of soup. These numbers shift depending on your sex, body size, age, and health, and the ranges published in medical references have actually been creeping upward in recent decades as average body weight has climbed. But the broad picture is that the organs responsible for keeping you alive add up to only a fraction of your total body mass, and a few of them punch far above their weight in terms of energy demand.
Typical Weights of Major Organs
Reference tables for organ weights come mostly from autopsy studies, since weighing organs in living people is not straightforward. Across multiple large studies, the numbers cluster in recognizable ranges. In a study of Zambian adults, the brain averaged about 1,335 grams in men and 1,228 grams in women, making it roughly 2.3 percent of total body weight in both sexes. The liver averaged around 1,285 grams in men and 1,368 grams in women. The heart weighed about 279 grams in men and 268 grams in women, representing less than half a percent of body weight.1PubMed Central. Correlation of Internal Organ Weights with Body Weight and Body Height in Normal Adult Zambians: A Case Study of Ndola Teaching Hospital
Below the big three, the lungs together weigh close to a kilogram, though the right lung is consistently heavier than the left, roughly 500 grams versus 440 grams in men. The kidneys are lighter than most people assume, averaging about 110 to 120 grams each. The spleen sits around 160 to 170 grams, though it varies wildly from person to person. And the pancreas, which plays such an outsized role in digestion and blood sugar control, weighs only about 80 to 100 grams in most adults.1PubMed Central. Correlation of Internal Organ Weights with Body Weight and Body Height in Normal Adult Zambians: A Case Study of Ndola Teaching Hospital
A large, more recent autopsy database suggests that median organ weights for several commonly weighed organs have increased compared to older reference tables, driven primarily by the upward trend in average body weight over the past several decades.2PubMed. Updating Normal Organ Weights Using a Large Current Sample Database That means organ-weight charts published in the 1970s and 1980s may underestimate what a pathologist sees on the table today.
Why Men’s and Women’s Organs Differ
Men’s organs tend to be heavier than women’s for almost every organ, even after accounting for the fact that men are on average bigger. The heart, brain, kidneys, and lungs all run heavier in men. The one notable exception is the liver, which is comparable in weight between men and women once body size is controlled for.2PubMed. Updating Normal Organ Weights Using a Large Current Sample Database
This pattern is remarkably consistent across populations. A cross-population analysis examining autopsy data from eight different groups found that male and female organ weights were so tightly coupled that male organ weight could be expressed as a straightforward function of female organ weight. The relationship held across diverse populations, with one noted exception in a dataset from India.3PubMed. Male/female weight of internal organs: examination across multiple populations So while the absolute numbers differ, the proportional relationships between organs stay fairly constant between the sexes.
How Body Size Shapes Organ Weight
Taller, heavier people have heavier organs, but the relationship is not as simple as “twice the body weight, twice the liver.” For organs like the heart, liver, and spleen, there is a strong positive link to body weight. For the lungs and kidneys, the link exists but is weaker.2PubMed. Updating Normal Organ Weights Using a Large Current Sample Database The brain is the odd one out: it barely tracks with body weight at all. A person who weighs 50 percent more than their neighbor does not have a 50 percent heavier brain. Brain weight correlates much more with age than with body size.
The mathematical details of how organs scale with height are revealing. Liver, lean body mass, and skeletal muscle scale roughly with the square of height, while brain mass scales with a much smaller exponent, around 0.83, meaning taller people have only slightly heavier brains. In women, the fraction of total body weight made up by the brain actually decreases as height increases.4PubMed Central. Scaling of human body composition to stature: new insights into body mass index When researchers looked at how organ mass relates to overall fat-free mass, they found the heart and brain had very low scaling exponents, while fat mass and the spleen scaled above one, meaning those tissues grow disproportionately as a person gets bigger overall.5PLoS ONE. Effect of Constitution on Mass of Individual Organs and Their Association with Metabolic Rate in Humans—A Detailed View on Allometric Scaling
In children, the scaling is different again. A large study of traumatic deaths in children from birth to age 12 found that body length was the best predictor of organ weight, better than age or total body weight, and established reference ranges broken down by both age and body length.6PubMed. Organ Weight Reference Ranges for Ages 0 to 12 Years This makes intuitive sense: two five-year-olds can vary enormously in size, but their height is a more stable index of their overall growth stage.
What Happens to Organ Weight as You Age
Aging shrinks most organs. In a study of elderly Japanese adults, including 50 centenarians, organ weights decreased with age in every organ measured, with two exceptions: the heart in men did not shrink, and the lungs did not lose weight in either sex. Undernutrition, which is common in very old age, compounded the effect, particularly for the heart and liver.7PubMed. Standard organ weights among elderly Japanese who died in hospital, including 50 centenarians
A broader analysis of age-related weight loss found that the reduction in body weight during later aging is accompanied by a coordinated loss of internal organ weight and volume. Rather than organs declining independently, the loss appears to follow a general pattern where each organ’s weight tracks roughly with overall body weight, even in decline.8PubMed. Organ/body weight loss with aging: evidence for co-ordinated involution
The brain deserves special mention. Unlike other organs, brain weight declines primarily with age rather than with changes in body weight. A person can maintain a stable body weight from their 40s into their 70s and still lose a meaningful amount of brain mass. The brain’s independence from body-weight trends makes it a useful marker for age-related changes when pathologists assess whether organ weights are normal at autopsy.2PubMed. Updating Normal Organ Weights Using a Large Current Sample Database
A large autopsy study from Tehran documented a similar overall pattern: organ weights generally decreased with age, with the exception of the heart and the prostate, both of which tended to increase.9PubMed. Study of the normal internal organ weights in Tehran’s population The prostate’s growth with age is driven by benign hyperplasia, a near-universal finding in older men. The heart’s resistance to shrinkage likely reflects a combination of increased workload (from stiffer arteries and higher blood pressure with age) and, in some cases, subclinical disease.
When Disease or Substance Use Alters Organ Size
Pathological conditions can push organ weights well outside normal ranges. Chronic alcohol misuse is a well-known driver. Autopsy data show that men who chronically misused alcohol had cardiomegaly (an enlarged heart) at rates of about 27 percent compared to 19 percent in controls, and hepatomegaly (an enlarged liver) at about 38 percent compared to 15 percent.10PubMed. Heart, liver and spleen pathology in chronic alcohol and drug users The liver enlargement is fatty infiltration and inflammation; the heart enlargement comes from direct toxic effects of alcohol on cardiac muscle.
Hormonal conditions can have dramatic effects as well. In acromegaly, where excess growth hormone is produced over years, the heart can become massively enlarged. Patients who died more than 10 years after the onset of acromegaly had a mean heart weight of about 618 grams, compared to roughly 348 grams in those who died within 10 years. Still, even in acromegaly the heart rarely exceeded twice the expected weight for the patient’s body size.11American Heart Journal. Pathology of the heart in acromegaly: anatomic findings in 27 autopsied patients
On the other end of the spectrum, starvation causes selective organ shrinkage. Animal research has shown that during prolonged fasting, the liver, kidneys, intestines, and lungs lose protein on a similar timeline regardless of initial body fat stores. The brain, stomach, and skin are relatively spared. In animals with more fat reserves, cardiac and skeletal muscle are also conserved for a longer period, but that protection disappears once fat stores are nearly exhausted.12PubMed. Sites of protein conservation and loss during starvation: influence of adiposity The body essentially sacrifices some organs to protect others, and the brain sits at the top of that hierarchy.
Athletic Training and Organ Growth
Exercise and high-calorie intake can increase the mass of internal organs beyond typical ranges without causing disease. A study of male college football players found that seniors had about 290 grams more liver mass, 80 grams more heart mass, and 90 grams more kidney mass compared to freshmen. When freshmen were followed for one year of overfeeding and intense physical training, their liver mass increased by about 200 grams and their heart and kidney mass increased by about 40 grams each. The ratio of organ mass to fat-free mass stayed constant, though, except for the brain, which did not grow. The body was getting bigger everywhere, and the organs kept pace.13International Journal of Sport Nutrition and Exercise Metabolism. Organ Size Increases With Weight Gain in Power-Trained Athletes
The heart specifically adapts to different types of training. A meta-analysis of cardiac structure in athletes found that endurance athletes, strength athletes, and those doing both all had thicker heart walls and larger internal heart dimensions than non-athletes. Strength-trained athletes had the thickest walls (a relative wall thickness of 0.44 compared to 0.36 in controls), while endurance athletes had the widest chamber diameters. Despite these structural changes, heart function remained normal in all groups: ejection fraction, fractional shortening, and the filling patterns measured by echocardiography were no different from those of sedentary people.14PubMed. The athlete’s heart. A meta-analysis of cardiac structure and function This is why the “athlete’s heart” can confuse an unwary clinician: the structural changes look alarming on a scan, but the function is perfectly healthy.
Organ Weight and Metabolic Demand
One of the most striking things about organ weights is how disproportionate they are to energy use. Your brain weighs about 2 percent of your body, but it consumes roughly 20 percent of your resting energy. The commonly cited estimates for resting metabolic rates of major organs put the heart and kidneys at about 440 kilocalories per kilogram per day, the brain at about 240, and the liver at about 200. Skeletal muscle, by contrast, burns only about 13 kilocalories per kilogram per day, and adipose tissue just 4.5.15PubMed Central. Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure16PubMed Central. Evaluation of specific metabolic rates of major organs and tissues: comparison between men and women
This means that a handful of organs weighing maybe 4 to 5 kilograms collectively account for the majority of the calories you burn at rest. It also has evolutionary implications. The “expensive tissue hypothesis” proposes that because brain tissue is so metabolically costly, the evolution of large human brains required compensating reductions in other metabolically expensive tissues, particularly the gut.17PubMed Central. The Expensive-Tissue Hypothesis in Vertebrates: Gut Microbiota Effect, a Review Whether the tradeoff is quite that neat is debated, but the basic point stands: organ size and metabolic demand are deeply intertwined, and shifts in one organ’s mass can ripple through the body’s energy budget.
How Organ Weights Are Actually Measured
Nearly all published reference values for human organ weights come from autopsies, which introduces some complications. Pathologists have long recognized that the cause and circumstances of death can alter what the organs weigh. When significant blood loss occurred before death, organ weights at autopsy were substantially lower than in controls: about 30 percent lower for the lungs, 28 percent for the spleen, 18 percent for the liver, and 14 percent for the kidneys.18PubMed Central. Effects of blood loss on organ attenuation on postmortem CT and organ weight at autopsy Congestion from drowning or congestive heart failure pushes weights up. Decomposition gases can also distort measurements, making post-mortem imaging estimates unreliable if putrefaction has set in.19Investigative Radiology. Noninvasive Estimation of Organ Weights by Postmortem Magnetic Resonance Imaging and Multislice Computed Tomography
For this reason, the best reference tables restrict their data to deaths from trauma or sudden cardiac events in otherwise healthy people, excluding anyone with organ-altering diseases. One widely cited European table drew from 684 adult autopsies of people who died from external causes and showed no pathological changes, and the authors stressed that such tables need to be updated regularly as population body sizes shift.20PubMed. Organ weight in 684 adult autopsies: new tables for a Caucasoid population
Non-invasive techniques are improving. MRI-based volume estimation has shown excellent agreement with actual organ weights in fetuses, newborns, and children, with correlations around 0.99 between estimated and actual weights, though accuracy drops for very small subjects under about 300 grams total body weight.21PubMed. A semi-automated method for non-invasive internal organ weight estimation by post-mortem magnetic resonance imaging in fetuses, newborns and children Converting volume to weight requires knowing the organ’s density, which varies slightly by organ: fetal brain tissue runs about 1.08 grams per cubic centimeter, while liver and lung tissue are around 1.15.22PubMed. Postmortem fetal organ volumetry using magnetic resonance imaging and comparison to organ weights at conventional autopsy In living adults, MRI and CT estimates are less precise. One study using pigs found that MRI-derived volumes of the liver, heart, kidneys, and brain correlated well with dissected weights, but they were not exact matches: MRI volumes overestimated heart weight by about 13 percent and brain weight by about 26 percent, while underestimating kidney weight by around 10 percent.23Journal of Animal Science. Body composition analysis of the pig by magnetic resonance imaging
Do Organ Weights Differ Across Racial and Ethnic Groups
This is a question pathologists and toxicologists have examined carefully, because organ weight tables are routinely used in forensic and clinical settings and need to be accurate for the populations they serve. A study building growth algorithms from autopsy data that included both Black and white individuals found no observable or statistically significant difference in organ weights between the two groups.24PubMed. Human organ/tissue growth algorithms that include obese individuals and black/white population organ weight similarities from autopsy data This stands in contrast to many other body-composition measurements that do differ between racial groups, such as bone density and limb proportions. The practical takeaway is that population-specific organ weight tables are driven far more by the average body size and nutritional status of a population than by its racial or ethnic makeup.
That said, pathologists still update tables regionally because body size norms do differ between countries and across eras. Tables from a 1994 Japanese study will not match tables from a 2020 American study, not because of inherent biological differences in organ size, but because average body weight in those populations has diverged considerably over time.
Why Organ Weight Matters in Transplant Surgery
The practical consequence of organ weight variability is perhaps most visible in transplant medicine. When matching a donor liver to a recipient, surgeons need the graft to be roughly the right size for the recipient’s body. A liver that is too small cannot handle the metabolic load and risks failure. One that is far too large may not physically fit in the abdominal cavity and can develop compression-related blood flow problems. The standard approach is to estimate the recipient’s expected liver volume from body surface area and aim for a graft that falls within an acceptable percentage of that estimate.25BioScience Trends. Donor-recipient matching in adult liver transplantation: Current status and advances
Similar size-matching considerations apply to heart and kidney transplants, though the tolerance ranges differ. The kidney is more forgiving of a size mismatch than the liver or heart, partly because recipients usually receive only one kidney and the body adapts by letting the single graft enlarge over time. Heart transplants are the least forgiving: a significantly undersized donor heart placed in a large recipient struggles from the start, and outcomes suffer when the mismatch is too wide. All of this depends on reasonably accurate organ-weight references, which is why the field invests so much effort in keeping those tables current.