# ­xkcd thread **URL:** \ **Category:** Cafe Society\ **Tags:** comic-strips\ **Created:** [May 28, 2020, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574 "2020-05-28T00:57:03Z")\ **Posts on this page:** 20\ **Page:** 219
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 31, 2025, 3:49am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4363 "2025-05-31T03:49:17Z")
The sinuses alone are what, like 2-3% of the volume alone? So being a bit stuffed up one day would probably put you over the threshold. I dunno, my total body mass easily varies by \>1% day-to-day and even more across a few days, despite me weighing myself under basically exactly the same conditions each time. As best I can tell most of this variation is from changes in water retention. Although the brain is probably less affected than other organs, plenty of the head’s total volume is just skin and muscle, which I’d expect to be as affected as anything. If an average head is 4 kg, 1% of that is just 40 grams. And really we should be thinking of deviations; if we’re just 20 grams “low” on one day, and 20 grams “high” on the next, that’s still 1%. For the record, this is all just personal speculation based on a limited amount of personal knowledge. Contrary to what some have claimed, I do not in fact have a personal collection of human heads in jars that I can draw inferences from. ETA: It would not shock me if the trimmings from a _haircut_ weighed \>40 g (I have very thick hair). ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 31, 2025, 4:00am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4364 "2025-05-31T04:00:45Z")
Consider also the possibility that I’m enraged due to someone trying to cut off my head in order to weigh it. My blood vessels will have dilated significantly, possibly by \>10% in average cross-sectional area. If my head typically contains 500 ml of blood, it will now contain 550 ml (taken from less important parts of my body), which is also enough to cause 1% variation. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [May 31, 2025, 6:58am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4365 "2025-05-31T06:58:41Z")
> **[Check Engine](https://xkcd.com/3096/)** [![](https://imgs.xkcd.com/comics/check_engine.png) ](https://imgs.xkcd.com/comics/check_engine.png) “They say it’s probably safe to keep orbiting for a while, but if it stays on or starts flashing we might have to call someone.” ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 31, 2025, 7:10am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4366 "2025-05-31T07:10:00Z")
One day we’ll be a Kardashev Type II civilization and Coca-Cola will use gravitational wave manipulators to engrave their logo into the Sun (even though it’s actually better suited to Pepsi). ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [May 31, 2025, 8:06am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4367 "2025-05-31T08:06:02Z")
> [@abcdefghij](#): > > Where is my double chin if not on my head? Below? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 31, 2025, 1:43pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4368 "2025-05-31T13:43:49Z")
> [@Dr.Strangelove](#): > > One day we’ll be a Kardashev Type II civilization and Coca-Cola will use gravitational wave manipulators to engrave their logo into the Sun (even though it’s actually better suited to Pepsi). Surely, it would be 6+? ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [May 31, 2025, 2:52pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4369 "2025-05-31T14:52:26Z")
Okay this strays farther afield but where better to nerd out on a question like this? 😀 Item the first. Accuracy of volumetric MRI. Different software using the same machines and same imaging protocols will [vary](https://pmc.ncbi.nlm.nih.gov/articles/PMC10726865/) by 5 to 10%. The second. Day to day variation. OTOH any true day to day is still the real weight of the head at that moment. But no, head mass should change little compared to the rest of the body. Cerebral blood flow does shift in various regions but total blood volume in the brain just has no space to increase. It is a confined space and increasing pressure … is bad. The sinuses don’t typically go from all air filled to socked in with fluid and pus. Maybe day to day a little mucosal thickening? But that is insignificant on scale. You are correct that muscles and various organs can change volume day to day, just with how much glycogen and obligate water is there, (skin not much but can vasodilate and increase blood volume a little), but the head actually has little of its volume or mass as muscle. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 31, 2025, 2:57pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4370 "2025-05-31T14:57:07Z")
> [@DSeid](#): > > but the head actually has little of its volume or mass as muscle. … Instead it’s mostly rocks and cheese. 😉 ---
**Author:** ![abcdefghij](https://avatars.discourse-cdn.com/v4/letter/a/43a26b/32.png) [@abcdefghij](https://boards.straightdope.com/u/abcdefghij)\ **Post date:** [May 31, 2025, 3:11pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4371 "2025-05-31T15:11:14Z")
> [@DSeid](#): > > The sinuses don’t typically go from all air filled to socked in with fluid and pus. Maybe day to day a little mucosal thickening? I dunno. Given how stuffy I feel this week, I figure my sinuses have to be good for at least 20%. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [May 31, 2025, 3:24pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4372 "2025-05-31T15:24:12Z")
Better than a hammer and sickle ---
**Author:** ![SunUp](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@SunUp](https://boards.straightdope.com/u/SunUp)\ **Post date:** [May 31, 2025, 3:30pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4373 "2025-05-31T15:30:53Z")
_The Man Who Sold the Moon_, right? ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [May 31, 2025, 3:46pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4374 "2025-05-31T15:46:43Z")
Yes, that’s it ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 31, 2025, 5:39pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4375 "2025-05-31T17:39:53Z")
> [@Chronos](#): > > Surely, it would be 6+? Uh, what? A Type 4 controls all energy in the known universe. What the heck is a Type 6+? Granted, I am assuming some future tech allows manipulation of gravity using energies a bit less than black hole scale. Or at least using stable micro black holes. Either way, something on the order of the sun’s energy output, rather than the galaxy or more. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [May 31, 2025, 5:42pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4376 "2025-05-31T17:42:32Z")
See > [@Dr.Strangelove](#): > > > [@Chronos](#): > > > > Surely, it would be 6+? > > Uh, what? See riffs above on _The Man Who Sold The Moon_ by Heinlein. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 31, 2025, 5:49pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4377 "2025-05-31T17:49:14Z")
In case anyone’s unfamiliar with the story: D. D. Harriman is a private businessman who’s driving the first manned mission to the Moon, and is securing funding wherever he can. He ends up selling rights to advertising on the Moon’s surface, visible from Earth, to a soft drink company who has no intention of using those rights, by hinting that 6+ (a fictitious rival soft drink brand) would buy them instead. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 31, 2025, 5:57pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4378 "2025-05-31T17:57:39Z")
> [@DSeid](#): > > Item the first. Accuracy of volumetric MRI. Different software using the same machines and same imaging protocols will [vary](https://pmc.ncbi.nlm.nih.gov/articles/PMC10726865/) by 5 to 10%. Yeah, like I said originally, no way you’re actually getting within 1% with an MRI. Though I see from the paper that they had the greatest variation when measuring specific brain structures. Well, that’s not too surprising. The “whole brain” volume was \<2% different. > [@DSeid](#): > > Maybe day to day a little mucosal thickening? But that is insignificant on scale. But we’re talking about only 1%–again, on the order of 40 grams. A Google search tells me that the surface area of the sinuses and nose are 100-200 cm^2. So you could add 15-30 grams just from a 1 mm difference. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 31, 2025, 5:59pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4379 "2025-05-31T17:59:39Z")
> [@Northern\_Piper](#): > > See riffs above on _The Man Who Sold The Moon_ by Heinlein Ahh! Perhaps suprirsingly, I’ve never read that particular Heinlein (though I’m aware of the advertising angle). I keep meaning to get the full collection and go through it. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [May 31, 2025, 6:37pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4380 "2025-05-31T18:37:21Z")
Hmmm. Total volume of the sinuses is roughly 20 to 25 ml. Go from all air filled to all fluid filled, complete opacification, which can happen over the course of a week with the onset of severe pansinusitis, can gain up to 25g. Limit case. 1 mm may sound like a little but in the spaces it is a lot. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 31, 2025, 9:02pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4381 "2025-05-31T21:02:32Z")
Well, I had found this paper: [https://www.nature.com/articles/s41598-024-66527-7](https://www.nature.com/articles/s41598-024-66527-7) [![Imgur](https://i.imgur.com/FAS7uXA.png "imgur.com") ](https://imgur.com/FAS7uXA) So I figured 1 mm was a fairly normal level of thickening. In any case, we’re getting pretty far afield of the thread topic 🙂 . Maybe 1% total head variation is a little on the high side, but I think a couple tens of grams difference day to day is plausible, and maybe more if you count hair and… a large double chin. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [May 31, 2025, 9:33pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/4382 "2025-05-31T21:33:37Z")
> [@Dr.Strangelove](#): > > In any case, we’re getting pretty far afield of the thread topic 🙂 When has that ever slowed down this thread ? 😁 [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=218) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=220)