In a world inhabited by primitive hunter-gatherer humans and dragons, one of the most respected trial by fires is to hunt a dragon by jumping through their mouth and killing it from inside the stomach. Understandably, the survival rate of such a trial is not high.

However, the question arises, how big would this dragon have to be? The hunter has to know the minimum size of dragon to find for their trial, otherwise they could get stuck halfway, and nobody alive wants to be stuck in a dragon's throat. Knowing the minimum size would also help the hunter find a suitable dragon easier, and it is also easier for a hunter to perform the feat on smaller, slightly weaker dragons than a behemoth.

This could also be useful information for their rivals. Oops. Who could have predicted the dragon was just a size too small?

The question: given the shoulder length of a human warrior, is there a rough formula for the minimum size a dragon has to be, for this human to be able to go through its esophagus and into its stomach?


  • the dragon has the same internal organ to body proportions as a standard lizard
  • externally, dragons have the same form as a standard lizard, difference being wings and a flamesac for fire breathing
  • size would be for the rough height, width, and length of its body and head, excluding its tail and wings.
  • the dragon's esophagus is the right diameter for that person to slide through with an allowance of +/- 5%. Sometimes you just have to squeeze through.
  • you can use metric or imperial for size. Assume the barbarians know unit conversion and politely measure dragons for suitability before each trial.
  • don't worry about the stomach acid. This is why it is called a trial by fire.


  • If you want to use calculations, you can use Billbo as an example. He is a healthy male of height 180cm, shoulder width 41 cm, and 71 kilograms of weight.

Diagram of a Dragon without its flamesac and wings:

enter image description here

Derived Algorithm from Answers so far:

Referencing Emilio's answer, the total length of dragon needed for a Billbo-sized hunter to do the trial for is 31 meters, the rough length of 2 sperm whales.

Thus, with Billbo as a reference, we know we require roughly 2 sperm whales of length per 1 Billbos, which equals 2. We call this number the Billbo Constant. Hunters can find their width in respect to Billbo, and multiply it by the Billbo constant to find how many sperm whales in length the dragon has to be.

Let's use Jojoe, the widest man in the tribe, as an example. Jojoe prays to the tribal gods before finding the great Billbo to compare lengths with. Jojoe finds his belly is 60 cm in diameter, versus Billbo's 41cm shoulders. With this comparison, Jojoe knows that he is 1.5 Billbos in width. He multiplies it by the Billbo Constant of 2, and knows that he must find a dragon that is at least 3 sperm whales from head to tail. Confident, he goes off in his adventure, mostly sure that he will not meet an ignoble end as a fishbone in a dragon's throat.

  • 2
    $\begingroup$ Chopping the organs to bits will definitely kill the dragon, but how is the warrior going to escape? If the skin is too tough to cut through from the outside, it will be the same from the inside! $\endgroup$
    – KeizerHarm
    Sep 11, 2022 at 7:30
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    $\begingroup$ @KeizerHarm good question. I think they would opt to go out the way they came in, unless they want to risk going out the other end! $\endgroup$
    – Enthu5ed
    Sep 11, 2022 at 10:59
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    $\begingroup$ I know you said to not worry about stomach acid, but you might want to consider breathing as well. I'm not sure if there'd be sufficient oxygen in a lizard's stomach, and any hydrochloric gas will be very dangerous to inhale. The trial by fire may need to be a speedrun. $\endgroup$
    – Drake P
    Sep 11, 2022 at 15:57
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    $\begingroup$ @DrakeP serious lung damage you say? REAL WARRIORS DO NOT WORRY cough about such wheeeeze trifles. Burns, suffocation, and serious lung damage. Such a trial really makes for an occupational hazard doesn’t it? $\endgroup$
    – Enthu5ed
    Sep 11, 2022 at 17:53
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    $\begingroup$ @DrakeP People can hold their breath for a long time. Take athletic swimmers as an example, who stay under water quite a while before they surface. If a warrior can hold their breath for 20 seconds, that's plenty of time to mortally wound a dragon and climb back out! $\endgroup$
    – EdvinW
    Sep 11, 2022 at 21:54

3 Answers 3


31 meters long, from head to tail.

I pasted your Diagram of a Dragon in MS Paint and inserted a straight line across the narrower visible section of the esophagus, right next to where the trachea gets touched by the line linking it to its label. Took note of the tools's measure of "number of pixels from picture edge to mouse cursor" at both ends of the line. They are:

144, 113

140, 121

Horizontal and vertical displacements are respectively 4 and 8 pixels.

The lenght of that line, following the Theorem of Pitagoras, is the square root of the sum of the squares of the horizontal and vertical displacements. That's 8.944 pixels.

If that corresponds to Billbo's shoulder length of 41cm, that means a pixel of your Diagram of a Dragon is 4.584cm long.

Taking just the horizontal displacement for an approximation, the tip of the head starts at 70 pixels, the curve of the tail at its rightmost is at 627 pixels, and the tip of the tail is at 513 pixels. So the whole dragon is approximately (627-70)+(627-513) = 671 pixels long.

Multiplying the length of the dragon in pixels by the length of one pixel in centimeters, we get 3075.8 cm.

So about 31 meters long, from head to extended tail.

  • $\begingroup$ Awesome. I wasn't sure we would use the diagram as an anatomically correct one, but on second thought, your usage of it is fair. If we do use the picture, this means the body length would be roughly 15 meters.So the formula could be something like 15m/0.41m * (shoulder width in meters). $\endgroup$
    – Enthu5ed
    Sep 14, 2022 at 15:24
  • $\begingroup$ bounty awarded, most relevant to what I needed, thanks! $\endgroup$
    – Enthu5ed
    Sep 16, 2022 at 15:24

The only animals which could swallow an adult human whole without tearing their bodies apart first are giant constrictor snakes, which squeeze their prey to death first before swallowing, to avoid the scenario in the question where the prey could damage their digestive system.

And large adult male sperm whales. If a human is oriented correctly, it can be swallowed whole and thus possibly alive by a large adult male sperm whale. I am not certain about the ability of smaller sperm whales.

However the story about James Bartley being swallowed alive by a sperm whale is fictional.




However, it should be possible for a large adult male sperm whale to swallow a man whole, and thus alive if they are live at the time.

In one scientific book a list of the normal and unusual contents found in the stomachs of sperm whales included a human cadaver. And the word cadaver indicates to me that it was someone wrapped up in a sack, weighted, and buried at sea to be later swallowed by the whale instead of someone alive when swallowed.

I once read a mention of a fight between whalers and the legendary great white whale Mocha Dick, a main inspiration for you-know-who, where Mocha Dick allegedly swallowed two whalers who fell into the water. I don't know if Mocha Dick actually swallowed them or they just fell into the water near his mouth and sank due to the weight of their clothing, and the witnesses imagined Mocha Dick swallowing them.

I once read of another incident where a harpooned sperm whale smashed a whale boat possibly by biting it in half, and then submerged carrying a man in its mouth. The other whalers must have though he would certainly drown or be eaten. But the whale came back up, tossed the living man onto floating wreckage, and dove again.

So if you were being attacked by a pack of wild animals would you rescue one of them which got injured? Maybe the whale didn't know that the human was one of its attackers.

Suppose you are walking through bushes when you feel a sudden stabbing pain in your back and you run away without looking back to see what's attacking you. Suppose you run into a bush and knock a bird's nest with a baby bird onto the ground, and stop to pick up the nest and bird and put them back in the bush, and then resume running for your life.

Wouldn't that be a very kind and considerate thing for you to do? And wasn't returning a man to the surface be a very kind and considerate thing for the whale to do while being attacked?

Anyway, I once read of a man who crawled down the throat of a dead large adult male sperm whale to reach the stomach. I think he would have been very stupid if he didn't have a rope tied to him and people ready to pull him out if he got stuck. Anyway his example seems to show that the throat of a large adult male sperm whale could be wide enough for the body of a man to pass through if in the correct orientation.

And I once read of a dead sperm whale tourist attraction where people could walk down the throat and into the stomach. Although I suspect that the operators of the attraction excavated to make the throat and stomach larger than when the whale was alive.

Anyway whale scientists who have dissected sperm whales of various sizes should have measured the diameters of the throats and stomachs of those whales and should have a good idea of the relationship between overall length and throat diameter.

This site claims it is very, very improbable for a living person to be swallowed alive by a sperm whale.

And some experts claim that it may theoretically be possible for a sperm whale to swallow a person whole, though there are two problems with this. One is that the sperm whale’s dagger-like teeth would likely kill the prey first, in which case you’d be long dead before suffocating in the whale’s several stomachs. But this point is rendered mostly null, as sperm whales only feed deep beneath the surface of the water and would never view humans as prey. So any accidental swallowing would have to derive from a rather bizarre sequence of events.


I note that Sperm whale teeth are actually rather blunt, not dagger like, so how much they hurt a person would depend on how hard the whale bit down. If the whale bit with full force it would be like having a drawbridge fall on you.

I note that healthy sperm whales have been found which were toothless, and others with malformed lower jaws which couldn't close on the upper jaw, and even one without a lower jaw. Apparently such whales feed by sucking in their prey and often don't bite on the prey.

It does offer some helpful stories about how some animals do manage to survive being swallowed alive.

And Wikipedia says:

While the veracity of the story is in question, it is physically possible for a sperm whale to swallow a human whole, as they are known to swallow giant squid whole.[11] However, such a person would be crushed, drowned or suffocated in the whale's stomach.[editorializing][citation needed] Like ruminants, the sperm whale has a four-chambered stomach. The first secretes no gastric juices and has very thick muscular walls to crush the food (since whales cannot chew) and resist the claw and sucker attacks of swallowed squid. The second chamber is larger and is where digestion takes place.[12]


So a large adult male sperm whale would be about the minimum size creature which could have a throat wide enough for an adult human to crawl down to reach the stomach and attack the stomach.

Could land animals that heavy exist?

The sperm whale is the largest toothed whale, with adult males measuring up to 20.7 metres (68 ft) long and weighing up to 80 tonnes (79 long tons; 88 short tons).[36][37][38] By contrast, the second largest toothed whale (Baird's beaked whale) measures 12.8 metres (42 ft) and weighs up to 14 tonnes (15 short tons).[39]


Though much larger ones have been reported.

Anyway, the most massive sauropod dinosaurs had weights estimated to be even heavier than the most massive sperm whale ever weighed by humans. Their necks are slender compared to their bodies, but some of them could have throats several feet wide.

Thus animals with enough mass to possibly have throats wide enough to swallow humans can walk on land on a planet with 1 g surface gravity and an atmosphere similar to that of present day Earth.

But of course no carnivorous land animal ever had more than a fraction of that size.

Though their throats should have been narrower, they do show that creatures with the weight of large adult male sperm whales, and thus possibly having throats as wide as sperm whales, could walk on land on a planet with a surface gravity of 1 g and an Earth like atmosphere.

And just for fun, here is a link to a image from a Prince Valiant comic strip in the 1930s where he fights a giant sea crocodile.


I think in the 198s there was rather similar plot with a giant lizard crawling toward Camelot. And in about 1960 or so I have a dim memory of a full page panel where a knight on foot with a sword faces a giant crocodile with the mouth opened wide enough it looked like the knight could have stepped inside the mouth.

And that reminds of an illustrated children's book from decades ago where a Chinese boy confronts a Chinese dragon that looks a lot like a crocodilian. I remember one illustration where the dragon's mouth is propped open with a pole and the boy is in the mouth walking toward the throat. As I remember, he goes inside the dragon to either kill it or help it.

  • $\begingroup$ Very cool! Thank you for the examples given, it’s very interesting and thorough. $\endgroup$
    – Enthu5ed
    Sep 11, 2022 at 14:01
  • $\begingroup$ note that whales being aquatic have much larger heads proportionally than any land animal could have. $\endgroup$
    – John
    Sep 12, 2022 at 21:40
  • $\begingroup$ Ironically, from the answer given based on lizard anaytomy, although the dragon needs to be double the length of a sperm whale, it turns out the dragon's body size perfectly corresponds to the size of a sperm whale (16m) to allow for an average sized man (shoulder width 41cm). $\endgroup$
    – Enthu5ed
    Sep 14, 2022 at 15:31
  • $\begingroup$ I think that just because sperm whales eat giant squid whole it doesn't mean they could swallow a human. Squids have no skelwton, the only hard parts in their bodies are the beak (and maybe an internal, bone-like structure in the mantle, but that's not very wide). A man would have their bones broken. A dead whale might have more relaxed throat muscles and less resistance to a man crawling inside, but still... $\endgroup$ Nov 1, 2023 at 18:07

The dragon needs to be the size of a sperm whale.

Reference: Swallowed by a Whale

Fair Use Quotation:

Late that night, working by lantern-light, the tired crewmen removed the stomach of the whale and slowly winched it to the deck for flensing. They were startled to notice movement inside the large sack, movement that looked like something living and breathing. The captain called the ship's doctor who made an incision in the tough flesh. And out slid the doubled up missing sailor, James Bartley, as if he were suffering from severe stomach cramps. He was alive, but unconscious.

The doctor ordered Bartley drenched with sea water, a treatment which restored his consciousness but not his reason, for he babbled incoherently.

Confined to a cabin for several weeks and bound so he could not injure himself in his wild flounderings, Bartley gradually regained his senses. Within a month he was able to relate what had happened to him in his terrifying experience.

Bartley said that as he was cast into the water from the long boat he saw a tremendous mouth open over him and he screamed as he was engulfed by it. He then felt sharp stabbing pains as he was swept across the teeth and then slid feet first down a slimy tube that carried him to the whale's stomach. He could breath, but the hot, fetid odor soon rendered him unconscious and the last thing he remembers was kicking as hard as he could at the soft, yielding stomach. Finally, he lapsed into unconsciousness until he again came to his senses almost a month later.

There was also a documented incident last year where lobster diver Michael Packard was swallowed alive by a humpback whale and lived to tell the tale. However, he was only in the mouth of the whale, not its stomach. Reference: Cape Cod Times

  • $\begingroup$ Thanks for answering ehbowen, and amazing quote! Just want to ask though - how do we know what size is just right for the hunter? That is to say, could fat Jojo get stuck trying to go through the same sperm-whale-sized dragon skinny Lulu went through? And can we assume a sperm whale has equal organ/esophagus to body ratio as a lizard/dragon? $\endgroup$
    – Enthu5ed
    Sep 11, 2022 at 2:57
  • $\begingroup$ Your world, your story. I can't tell you how to make a dragon 'realistic'. But if you write it as being this size, perhaps with an oblique reference to the real-world events I've noted, I as a reader would willingly suspend my disbelief...provided the rest of the story held my attention. Given your first paragraph which states that this is a common trial by ordeal, I'd imagine new candidates learn quickly by observing the survivors...else they become victims! $\endgroup$
    – ehbowen
    Sep 11, 2022 at 3:32
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    $\begingroup$ Yes, a sperm whale sized dragon could probably fit most people. But the problem is your answer can’t help these hunters with the scenario where they can’t find a whale-sized dragon, but see an elephant sized one. Can they still fit? We know the upper bound, but is a sperm-whale sized dragon the lower bound? $\endgroup$
    – Enthu5ed
    Sep 11, 2022 at 3:43
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    $\begingroup$ Surely part of the trial is risk assessing dragon size x your own size (shoulder girdle but also shape and bulk of armour)? Lulu can pick a smaller dragon, easier to defeat, and perhaps increase her chances with streamlined armour and a hefty layer of lard (mmmm… lard!). Jojo has to search for a bigger dragon, but will end up with a more spectacular trophy if he succeeds. $\endgroup$
    – Ottie
    Sep 11, 2022 at 4:34
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    $\begingroup$ The story about James Bartley is fiction disguised as fact. And Michael Packard was not sawllowed alive because he didn't go down the throat. $\endgroup$ Sep 11, 2022 at 5:33

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