Fact Check

Was the Weight of a Human Soul Determined to Be 21 Grams?

No credence should be given to the notion that experiments intended to measure the weight of a human soul proved anything.

Published Oct 26, 2003

A physician once placed dying patients upon a scale and determined the weight of the human soul to be 21 grams.
What's True

A doctor in the early 20th century weighed several patients at the moment of death in order to determine the weight of their departing souls.

What's False

These experiments were extremely flawed and demonstrated nothing credible about the human soul or post-mortem weight loss.

Most of those of a religious bent believe in life everlasting for the faithful, a continuation of the life force that reaches far beyond the limitations of mortal flesh. In such belief systems, death is not an end but a transformation: though people shed their corporeal selves at the moment of demise, that which made them unique beings lives on to rejoin the Creator. We call this intrinsic personhood "the soul," an entity described in the dictionary as "The immaterial essence, animating principle, or actuating cause of an individual life."

Yet as much as we believe in the concept of "soul," this life spark remains strictly an article of faith. As central as it is to our perception of ourselves, it can't be seen or heard or smelled or touched or tasted, a state of affairs that leaves some of us uneasy. Without the soul, dead is dead. But if it could be proved to exist, a great deal of anxiety over what happens to us when we die would be vanquished.

Enter Dr. Duncan MacDougall of Haverhill, Massachusetts, in the early 20 century:

Those who believe that the body becomes lighter [at the moment of death] seem to think that the soul has weight, weight that must of necessity depart with it, and — with that brisk disregard of strict veracity which so frequenly marks discussions of this nature — have claimed that dying men, at the very moment of their decease, have been placed on delicate scales that have recorded their mortuary degravitation. But these persons have never been able to specify in just what ghoulish laboratory this took place, or what private home was so interestingly equipped, or the names and addresses of the relatives who so commendably placed scientific and religious curiosity before sentimental concern for the patient's comfort.1

The doctor postulated the soul was material and therefore had mass, ergo a measurable drop in the weight of the deceased would be noted at the moment this essence parted ways with the physical remains. The belief that human beings are possessed of souls which depart their bodies after death and that these souls have detectable physical presences were around well before the 20th century, but claims that souls have measurable mass which falls within a specific range of weights can be traced to experiments conducted by Dr. MacDougall in 1907.

Dr. MacDougall, seeking to determine "if the psychic functions continue to exist as a separate individuality or personality after the death of brain and body," constructed a special bed in his office "arranged on a light framework built upon very delicately balanced platform beam scales" sensitive to two-tenths of an ounce. He installed upon this bed a succession of six patients in the end stages of terminal illnesses (four from tuberculosis, one from diabetes, and one from unspecified causes); observed them before, during, and after the process of death; and measured any corresponding changes in weight. He then attempted to eliminate as many physiological explanations for the observed results as he could conceive:

The patient's comfort was looked after in every way, although he was practically moribund when placed upon the bed. He lost weight slowly at the rate of one ounce per hour due to evaporation of moisture in respiration and evaporation of sweat.

During all three hours and forty minutes I kept the beam end slightly above balance near the upper limiting bar in order to make the test more decisive if it should come.

At the end of three hours and forty minutes he expired and suddenly coincident with death the beam end dropped with an audible stroke hitting against the lower limiting bar and remaining there with no rebound. The loss was ascertained to be three-fourths of an ounce.

This loss of weight could not be due to evaporation of respiratory moisture and sweat, because that had already been determined to go on, in his case, at the rate of one sixtieth of an ounce per minute, whereas this loss was sudden and large, three-fourths of an ounce in a few seconds. The bowels did not move; if they had moved the weight would still have remained upon the bed except for a slow loss by the evaporation of moisture depending, of course, upon the fluidity of the feces. The bladder evacuated one or two drams of urine. This remained upon the bed and could only have influenced the weight by slow gradual evaporation and therefore in no way could account for the sudden loss.

There remained but one more channel of loss to explore, the expiration of all but the residual air in the lungs. Getting upon the bed myself, my colleague put the beam at actual balance. Inspiration and expiration of air as forcibly as possible by me had no effect upon the beam. My colleague got upon the bed and I placed the beam at balance. Forcible inspiration and expiration of air on his part had no effect. In this case we certainly have an inexplicable loss of weight of three-fourths of an ounce. Is it the soul substance? How other shall we explain it?2

MacDougall repeated his experiment with fifteen dogs and observed that "the results were uniformly negative, no loss of weight at death." This result seemingly corroborated MacDougall's hypothesis that the loss in weight recorded as humans expired was due to the soul's departure from the body, since (according to his religious doctrine) animals have no souls. (MacDougall's explanation that "the ideal tests on dogs would be obtained in those dying from some disease that rendered them much exhausted and incapable of struggle" but "it was not my fortune to get dogs dying from such sickness" led author Mary Roach to observe that "barring a local outbreak of distemper, one is forced to conjecture that the good doctor calmly poisoned fifteen healthy canines for his little exercise in biological theology.")

In March 1907 accounts of MacDougall's experiments were published in the New York Times and the medical journal American Medicine, prompting what Mary Roach described as an "acrid debate" in the latter's letters column:

Fellow Massachusetts doctor Augustus P. Clarke took MacDougall to task for having failed to take into account the sudden rise in body temperature at death when the blood stops being air-cooled via its circulation through the lungs. Clarke posited that the sweating and moisture evaporation caused by this rise in body temperature would account both for the drop in the men's weight and the dogs' failure to register one. (Dogs cool themselves by panting, not sweating.) MacDougall rebutted that without circulation, no blood can be brought to the surface of the skin and thus no surface cooling occurs. The debate went on from the May issue all the way through December ...3

It would take a great deal of credulity to conclude that MacDougall's experiments demonstrated anything about post-mortem weight loss, much less the quantifiable existence of the human soul. For one thing, his results were far from consistent, varying widely across his half-dozen test cases:

  • "[S]uddenly coincident with death . . . the loss was ascertained to be three-fourths of an ounce."
  • "The weight lost was found to be half an ounce. Then my colleague auscultated the heart and found it stopped. I tried again and the loss was one ounce and a half and fifty grains."
  • "My third case showed a weight of half an ounce lost, coincident with death, and an additional loss of one ounce a few minutes later."
  • "In the fourth case unfortunately our scales were not finely adjusted and there was a good deal of interference by people opposed to our work . . . I regard this test as of no value."
  • "My fifth case showed a distinct drop in the beam requiring about three-eighths of an ounce which could not be accounted for. This occurred exactly simultaneously with death but peculiarly on bringing the beam up again with weights and later removing them, the beam did not sink back to stay for fully fifteen minutes."
  • "My sixth and last case was not a fair test. The patient died almost within five minutes after being placed upon the bed and died while I was adjusting the beam."

So, out of six tests, two had to be discarded, one showed an immediate drop in weight (and nothing more), two showed an immediate drop in weight which increased with the passage of time, and one showed an immediate drop in weight which reversed itself but later recurred. And even these results cannot be accepted at face value as the potential for experimental error was extremely high, especially since MacDougall and his colleagues often had difficulty in determining the precise moment of death, one of the key factors in their experiments. (MacDougall later attempted to explain away the timing discrepancies by concluding that "the soul's weight is removed from the body virtually at the instant of last breath, though in persons of sluggish temperament it may remain in the body for a full minute.")

Dr. MacDougall admitted in his journal article that his experiments would have to repeated many times with similar results before any conclusions could be drawn from them:

If it is definitely proved that there is in the human being a loss of substance at death not accounted for by known channels of loss, and that such loss of substance does not occur in the dog as my experiments would seem to show, then we have here a physiological difference between the human and the canine at least and probably between the human and all other forms of animal life.I am aware that a large number of experiments would require to be made before the matter can be proved beyond any possibility of error, but if further and sufficient experimentation proves that there is a loss of substance occurring at death and not accounted for by known channels of loss, the establishment of such a truth cannot fail to be of the utmost importance.2

Nonetheless, MacDougall believed he was onto something — four years later the New York Times reported in a front-page story that he had moved on to experiments which he hoped would allow him to take pictures of the soul:

Dr. Duncan MacDougall of Haverhill, who has experimented much in the observation of death, in an interview published here to-day expressed doubt that the experiments with X rays about to be made at the University of Pennsylvania will be successful in picturing the human soul, because the X ray is in reality a shadow picture. He admits, however, that at the moment of death the soul substance might become so agitated as to reduce the obstruction that the bone of the skull offers ordinarily to the Roentgen ray and might therefore be shown on the plate as a lighter spot on the dark shadow of the bone.Dr. McDougall is convinced from a dozen experiments with dying people that the soul substance gives off a light resembling that of the interstellar ether. The weight of the soul he has determined to be from one-half ounce to nearly an ounce and a quarter.4

<!--This article prompted someone to pen an unsigned, tongue-in-cheek editorial expressing substantial skepticism about the then-current fad for weighing souls and photographing auras, published in the Times the following day:

The world need not wait for the results of experiments about to be conducted by Dr. DUNCAN MacDougall of Haverhill, Mass., in obtaining pictures of the human soul. Anybody can do it. At least that is the confident announcement of Dr. W.J. KILNER of London, whose methods Dr. MacDougall and Dr. PATRICK S. O'DONNELL, the X-ray expert of Chicago, seem to have copied. Get some of Dr. KILNER's dye which he calls "dicyanin"; make a screen of glass, coat it with collodion and gelatine mixed with the dye, and uncover this sensitized screen in the gloaming before a select circle of friends.

Their auras, which in the half-half-light are visible through the screen to the keenly imaginative, may then be analyzed and classified. Their colors may be seen, especially if the owners of the auras be dull or mentally defective; then a bluish tendency is perceptible. The figure of the body projected upon the screen assumes not only its physical contour but the outlines of a radiographic emanation, of which one band is dark — this is the Etheric Double; the next is the Inner Aura, which often penetrates the Etheric Double and swathes the body; finally we have the Outer Aura, extremely variable, tremulous, and dissolving into the prosaic air. Three "standard" auras of different widths for men, women, and children have been defined. The auras vary from the standard or norm in conditions of health and sickness, so that Dr. KILNER is hopeful that their variations, noted by their effect upon the complementary colors and the eye's "color sensitive nerves" may be useful in locating the sites of pain and disease.

We have already printed some of Dr. KILNER's diagrams of the soul. We rely upon Drs. O'DONNELL and MacDougall for further authentic photographs and weights of the animating power, the etheric projection, the current of life, the last breath, the soul substance, or whatever it may be called, to make possible, in this halcyon and fatuous Summer season, a substitute for the customary word-pictures of the sea-serpent.5

Predictably, there were those who interpreted the editorial as one meant literally rather than ironically and expressed their outrage that experiments in photographing the human aura should be so misrepresented by the Times:

To the Editor of The New York Times:
Neither Dr. W. J. Kilner of London, nor Dr. MacDougall of Haverhill, Mass., nor Dr. Patrick S. O'Connell of Chicago has ever claimed that the atmosphere surrounding the human body represents the soul. None of these gentleman has ever claimed that he was able to obtain photographs of the atmosphere surrounding the body. All this talk has emanated from the heated brain of a highly imaginative newspaper reporter, but has no foundation in facts, and I am sorry for the man who palmed off this editorial on your good self . . .6


MacDougall seems not to have made any more experimental breakthroughs regarding the measurement of the human soul after 1911 (at least, none considered remarkable enough to have been reported in the pages of the New York Times), and he passed away in 1920. Nonetheless, his legacy lives on in the oft-expressed maxim that the human soul weighs 21 grams. (At the moment of death, MacDougall's first test subject decreased in weight by three-fourths of an ounce, which is 21.3 grams.)

What to make of all this? MacDougall's results were flawed because the methodology used to harvest them was suspect, the sample size far too small, and the ability to measure changes in weight imprecise. For this reason, credence should not be given to the idea his experiments proved something, let alone that they measured the weight of the soul as 21 grams. His postulations on this topic are a curiosity, but nothing more.

An interesting counterpoint to this item is another widespread belief of those long-ago times, one which held that the human body gained weight after death — the exact opposite of what Dr. MacDougall was attempting to prove:

More prevalent is the other belief, expressed in the phrase "dead weight," that a body weighs more after death. But it only seems to weigh more. We carry our own bodies about so easily that we are unaware of what an exertion it really requires. And when, in some emergency that forces us to bear the additional weight of another body, we feel a gravitational pull of from two hundred and fifty to three hundred pounds, we are astonished and assume that the other body has somehow acquired additional heaviness. The weight of a corpse, or even of an amputated limb, is startling when felt for the first time. A husky man, flourishing his arms about, has no idea that they weigh as much as twenty-pound sacks of sugar; and a jitterbugging girl doesn't realize that she is throwing a couple of forty-pound legs around as if they were ping-pong balls.1

Sightings:   The title of the 2003 film 21 Grams was taken from this belief.


    1.   Evans, Bergen.   The Natural History of Nonsense.<     New York: Vintage Books, 1946   (pp. 129-130).

Iserson, Kenneth V.   Death to Dust: What Happens to Dead Bodies?     Tucson, AZ: Galen Press, 1994.   ISBN 1-883620-07-4.

2.   MacDougall, Duncan.   "The Soul: Hypothesis Concerning Soul Substance Together with Experimental Evidence of The Existence of Such Substance."     American Medicine.   April 1907.

3.   Roach, Mary.   Stiff: The Curious Lives of Human Cadavers.     New York: W.W. Norton, 2003.   ISBN 0-393-05093-9   (pp. 173-175).

The New York Times.   "Soul Has Weight, Physician Thinks."     11 March 1907   (p. 5).

The New York Times.   "The Human Aura Has at Last Been Photographed."     5 February 1911   (p. SM8).

4.   The New York Times.   "As to Picturing the Soul."     24 July 1911   (p. 1).

5.   The New York Times.   "Picturing the Soul."     25 July 1911   (p. 6).

6.   The New York Times.   "Aura and Soul."     28 August 1911   (p. 6).

The New York Times.   "He 'Weighed Human Soul.'"     16 October 1920   (p. 13).

David Mikkelson founded the site now known as snopes.com back in 1994.