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How big can a person be while retaining all the functions of all their organs (including bones)? I am wondering if it is possible for large people to exist without compromising some part of their body. If someone invented a scaling machine (for example, Ant-Man), what would be the limit on how big a human could be scaled?

Here are the requirements: The human must be able to function like a normal human in an earth-like environment.

Being able to function normally means being able to do the following things without additional support or biological changes:

  • Live
  • Walk
  • Breathe
  • Eat
  • Sleep
  • Talk
  • Think
  • Do anything a normal person can do

Being more susceptible to injury is okay, as long as the injury is not directly caused by the size. For example, falling down and cracking your skull is directly caused by the ground, not by size. The spine spontaneously snapping because of the weight of the torso is directly caused by abnormal size.

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  • $\begingroup$ Just a note: I don't care how they got so big. $\endgroup$
    – Bilbo Baggins
    Jun 13, 2019 at 3:35
  • $\begingroup$ That question is related, but there are some subtle differences. For example, the ratio of surface area inside of the lungs to the volume of the human would greatly decrease in a hypothetical "scaling machine" but not in a seperate species. $\endgroup$
    – Bilbo Baggins
    Jun 13, 2019 at 3:52
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    $\begingroup$ Considering the tallest man Robert Wadlow ( 2.72m ) had to wear leg braces and had little feeling in his legs and feet, I don't think your going to be much larger if you simply scaled a human body up. It would require biological changes to make them truly giant. $\endgroup$
    – Shadowzee
    Jun 13, 2019 at 4:26
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    $\begingroup$ Are you assuming Earth gravity, or would you extend this to giant humans in low or zero gravity environments (a big space colony for example)? $\endgroup$
    – Hypnosifl
    Jun 13, 2019 at 4:34
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    $\begingroup$ I read an article in the late 1980s- and have searches for it several times since without success, where the authors had done calculations showing that a 10-ft tall human-shaped polymer object would suffer catastrophic structural damage if tipped over and impacting the ground. Further, this calculated height did depend on the universal gravitational constant, but not on local gravity. In other words, if you fall-down-go-boom on earth, the moon, Jupiter, even a decent sized asteroid, and you are more than 10 foot tall, you will crack your skull and other bones beyond recovery. (cont'd) $\endgroup$
    – cobaltduck
    Jun 13, 2019 at 11:44

3 Answers 3

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The main problem will be the square–cube law: If you scale something equally in all dimensions, the mass increases as the cube of the scale, while the surface and cross-section areas only scales with the square of the law.

This means that if you double the dimensions of a human being, its weight will be octupled, while the muscle and cross sections will only be quadrupled. Each square inch of muscle or bone cross section will have to carry twice the weight. Essentially, this will be like carrying another person on your back all the time. Also, the surface area of the lungs will be quadrupled, while the blood volume will be octupled, meaning that it will be harder to oxegynate the blood.

What is the limit that a human could feasibly be enlarged giving this increased strain? This is difficult to estimate, but there is a reason why land animals don't come larger than they are. The largest bipedal animal ever is probably the Tyrannosaurus Rex. The largest known specimen of T. Rex has been estimated to have been about 8.8 metric tons. Given that T. Rex was better built to carry this much weight than a scaled-up human, the limits from the square-cube law may be estimated to about 8 tons. This is roughly 100 times the weight of a 180 cm tall man, meaning that the scale would be the cube root of 100, or 4.64, for a height of 8.35 meters. This being would be able to carry objects weighing 4.64 squared = 21.5 times as much as a normal human could in his hands; say 500 kg. His arms, however, would each weight in at about 6% of the body mass, or 500-550 kg. This giant would hence barely be able to lift his own arms.

Other factors may limit the size. For one, the heart would have to pump blood 4-5 times higher, which would require that blood be pumped out at a higher pressure, which in turn would imply a relatively larger heart size. While T-Rex was big, it wasn't taller than 3.5-4.0 meters at the hip - less than half that of our enlarged human.

Given these further limitations, I would guesstimate that the largest feasible scale for a human will be at most x4, for a height of 7m20cm, with a mass of 5.120 kg. With a slightly more squat build, call it 7m and 5 tons.

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I'd say the minimum height for the largest human might be 9 feet. Robert Wadlow reportedly had great physical strength until his death. It is important to note he had little feeling in his legs and feet. I would imagine at reaching 9 feet in the 'scaling' process, the subject would experience significant loss of feeling in both the legs and arms.

The minimum weight might be ~1041 pounds. Robert Earl Hughes who reached this weight could reportedly walk in a limited capacity. Eddie Hall holds the world record for dead-lifting at 1,102 pounds, so this seems possible. Important note: Eddie Hall almost died once when attempting the dead-lift world record. He burst blood vessels in his head and collapsed.

If you are looking for super sniffing power: the largest nose ever is 8.8 cm, held by Mehmet Özyürek.

https://en.wikipedia.org/wiki/Robert_Wadlow https://en.wikipedia.org/wiki/Robert_Earl_Hughes https://en.wikipedia.org/wiki/Eddie_Hall https://en.wikipedia.org/wiki/Mehmet_%C3%96zy%C3%BCrek

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  • $\begingroup$ Based on Robert Hughes, I did some math to find the limit of the square-cube rule. Robert's feet supported 5 pounds per cm2. Thus, the limit on weight (w) is 5 times the surface area of the feet (s). The first equation would be simple: w = 5s. Weight is the size of the person to the third power, so w = h^3. Surface area is the size to the second power, so s = h^2. Substituting back into the first equation, we have h^3 = 5h^2, so h = 5. Therefore, the limit of the square-cube rule is 5 times the original size. $\endgroup$
    – Bilbo Baggins
    Jun 13, 2019 at 18:20
  • $\begingroup$ Based on this math, Klaus' answer is correct based on the square-cube law, but your answer was still helpful so I will upvote it. $\endgroup$
    – Bilbo Baggins
    Jun 13, 2019 at 18:26
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IMHO it should be possible to double the weight/strength ratio, or cut the strength/weight ratio in half, without too much extra strain on someone.

A person of average height who weighs twice as much as an average person would have twice the stress on his muscles and bones. And I know such a man who took walks up to about 8,000 feet (2.4 kilometers) before he lost a lot of weight. Some humans who have twice as much weight as normal persons of their height can function in modern society, even if they would be less successful in a hunter-gatherer society where more activity was required.

If someone six feet (1.82 meters) tall weighing 180 pounds (81.64 kilograms) is doubled in dimensions, he will be twelve feet (3.65 meters) tall and weigh eight times as much, or 1440 pounds (653 kilograms). His bones and muscles would have twice the dimensions and thus four time the cross section area as before, and would have to support eight times the weight, and thus have twice the weight stress as before.

And if that is roughly equivalent of a man six feet (1.82 meters) tall weighing 360 pounds (163 kilograms), then the double dimension twelve foot tall man should be able to function reasonably well.

but on the other hand, it is hard to find evidence to support the idea that a man that tall would function well. There have been a number of men over seven feet (2.13 meters) tall due to their genes, and many of them were quite strong. But most men and women who were extremely tall were so because of abnormal medical conditions, and did not function well, and had health problems.

The Guinness Book of World Records lists the Scottish-Canadian giant Angus MacAskill (1825-1863) as the tallest non-pathological giant, and the strongest man who ever lived. He was 7 feet 7 inches (2.31 meters) tall.

On a third hand, there are legends of even taller men who were reasonably strong and healthy.

The Philistine warrior Goliath was described as "four cubits and a span" (6 feet 9 inches, or 2.06 meters) or less plausibly as "six cubits and a span" (9 feet 9 inches, or 2.97 meters).

Georgios Maniakes was a famous eastern Roman or "Byzantine" general in about 1030 to 1043 who was alleged to have been eight feet (2.43 meters) tall.

The Roman emperor Maximinus (c. 173-238) was a Thraco-Roman peasant from Moesia (in the region of modern Serbia & Bulgaria) who joined the Roman army and usurped the throne in 235 and was killed in 238 aged about 65. Maximinus was allegedly super strong and eight and a half feet (2.59 meters) tall.

On a fourth hand, every human proven to be over 7 feet 7 inches (2.31 meters) tall, and some shorter than that, reached their height due to pathological conditions and most of those were unhealthy and had various size related medical problems.

On a fifth hand, there was the Giant of Castelnau. Three bone fragments were excavated in a bronze age cemetery in Castelnau-le-Lez, France, in 1890. They were estimated to be from a human about 3.50 meters (11 feet 6 inches) tall. If that is correct, that person would have been healthy enough and lived long enough to grow very long bones in a prehistoric era.

https://en.wikipedia.org/wiki/Giant_of_Castelnau1

On a sixth hand, there was the extinct ape genus Gigantopithecus which may have walked on two legs or four legs. Some scientists believe that they were about 1.8-2 meters (5.9-6.6 feet) tall and weighed 180-300 kilograms (400-660 pounds). Other scientists believe they might have been much larger, standing up to 3 meters (9.8 feet) tall and weighed up to 540-600 kilograms (1,190-1,320 pounds). They are popularly imagined to be up to 12 feet tall. But Gigantopithecus almost certainly didn't have human body proportions anyway.

I suggest that you study the lists of the tallest humans who ever lived and then find out about the health problems many of them faced.

https://en.wikipedia.org/wiki/List_of_tallest_people2

And possibly also study the lists of heaviest humans and find out about their health problems.

https://en.wikipedia.org/wiki/List_of_heaviest_people3

It seems to me that if a group of humans become genetically adapted or scientifically modified to change their proportions to better fit their size, they could be healthy in gravity similar to Earth's gravity with average heights of about seven feet (2.13 meters), eight feet (2.43 meters), nine feet (2.74 meters), etc, and still look fairly similar to normal sized humans with only slightly different proportions.

But it seems much less plausible to me that humans living in a one Earth gravity environment could be twelve feet (3.65 meters), or eighteen feet (5.48 meters), or twenty four feet (7.31 meters) tall, and still closely resemble normal sized humans.

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