# What is the Standard Deviation of Penis Size? **URL:** \ **Category:** Factual Questions\ **Created:** [February 4, 2005, 6:08am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334 "2005-02-04T06:08:58Z")\ **Posts on this page:** 19\ **Page:** 2
**Author:** ![hyjyljyj](https://avatars.discourse-cdn.com/v4/letter/h/0ea827/32.png) [@hyjyljyj](https://boards.straightdope.com/u/hyjyljyj)\ **Post date:** [February 5, 2005, 11:13am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/21 "2005-02-05T11:13:46Z")
> [@Washoe](#): > > Well, I tried Googling “penis size” and “standard deviation.” I really should have tried this first. I guess the reason that it didn’t occur to me to do so was because none of the pages in Cecil’s links contained this information, so I just blindly assumed that it wasn’t out there. OK, that does it. After all these years, and at the risk of being flamed and forever branded a leprous heretic, I’m finally gonna ask it. With almost all the folks who frequent this forum and others like it standing proudly behind their critical reasoning ability and helathy scientific skepticism, what is up with the slavish references to the person called Cecil Adams as “The Great Master”, “he who is incapable of error”, etc. and to oneself as a “member of the teeming masses” who worship his supposed infallibility? I have, quite literally for a period of years, endeavored to ascertain whether the obsequious accolades being showered upon the column’s author are tongue-in-cheek or for real. And I can’t. Maybe I’m in denial, afraid to believe they’re actually in earnest. I mean, to blindly assume that a bit of information simply does not exist purely because there are no links to it in this or that person’s database ought to be alarming to everyone reading this. This level of unquestioning faith is rarely accorded to anyone, even to God himself here. Is everyone kidding, or what? Sentences from otherwise highly intelligent people that start with the words “Not that I would ever dream of insinuating, hinting or even merely suggesting in any way that The Master had made a mistake,…” simply baffle me. He’s human, after all. An extremely bright human with a well above-average helping of integrity, reliabililty, humor, consistency and an uncanny ability to track down the…er…straight dope on an almost endless variety of topics, yes. But human all the same. Of course he could make, has made and will again make a mistake. Why put so much pressure on the man? Hasn’t he been kind to us all? 🙂 ---
**Author:** ![Roches](https://avatars.discourse-cdn.com/v4/letter/r/bc8723/32.png) [@Roches](https://boards.straightdope.com/u/Roches)\ **Post date:** [February 5, 2005, 1:59pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/22 "2005-02-05T13:59:58Z")
The ‘definitive survey’ online is self-reported and hence subject to exaggeration. I think the author’s choice to use millimeters rather than inches is intended to help counteract this (and to improve precision), but it’s also quite likely that many subjects simply convert their ‘known’ measurement to millimeters and report that, or add a few millimeters. Also, the sample is not truly random, even if it is well-distributed among different groups, because it is comprised only of those who visit the website and then choose to submit a report. Even if men who are confident about their size are only slightly more likely to submit reports than those who are not, the results will be skewed. Likewise, even if only a small percentage of those who are not satisfied with their results add a few millimeters somehow, the final result will be inaccurate. A few very exaggerated or totally false reports that are still included (it’s much easier to do this on the Internet) will increase the average and SD considerably. The appropriate Wikipedia entry says this about the ‘definitive survey’, and includes only one set of SD information, that from the Kinsey report (with SD = 0.77"). ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [February 5, 2005, 5:32pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/23 "2005-02-05T17:32:51Z")
> [@hyjyljyj](#): > > With almost all the folks who frequent this forum and others like it standing proudly behind their critical reasoning ability and helathy scientific skepticism, what is up with the slavish references to the person called Cecil Adams as “The Great Master”, “he who is incapable of error” It’s ironic. And I do mean the _real_ definition of irony (as TGM would know) rather than the popular notion of “coincidentally unfortunate”. How dry is the average sense of humor around here? Lemme put it this way: I can’t tell Steven Wright from Conan O’Brian. ---
**Author:** ![alterego](https://avatars.discourse-cdn.com/v4/letter/a/6bbea6/32.png) [@alterego](https://boards.straightdope.com/u/alterego)\ **Post date:** [February 5, 2005, 5:39pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/24 "2005-02-05T17:39:43Z")
Obligatory Wikipedia link: [Penis size](http://en.wikipedia.org/wiki/Penis_size) (NSFW) ---
**Author:** ![CynicalGabe](https://avatars.discourse-cdn.com/v4/letter/c/3e96dc/32.png) [@CynicalGabe](https://boards.straightdope.com/u/CynicalGabe)\ **Post date:** [February 5, 2005, 9:20pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/25 "2005-02-05T21:20:38Z")
Its not the size of the boat, its the motion in the ocean… ---
**Author:** ![threemae](https://avatars.discourse-cdn.com/v4/letter/t/5f9b8f/32.png) [@threemae](https://boards.straightdope.com/u/threemae)\ **Post date:** [February 6, 2005, 1:25am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/26 "2005-02-06T01:25:35Z")
> [@ultrafilter](#): > > Sure they do. That’s why it’s called the normal distribution. > > Porn stars are a small sample group and not selected at random, so there’s not much you can infer about the general population from them. Well, I’m damn sure that I’ve seen more than a few 10 inch plus penises. From the ansell link: xbar=5.877 st. dev.=.825 10 incher has a z-score of 4.99, which coresponds to a proportion of 2.87e-7, or 860 people world-wide with a 10 inchers. The point here being that normal distributions don’t seem to necessarily exist in real life. I tend to suspect that this distribution is much flater with more people lying in extreme situations than predicted by a Gaussian distribution. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [February 6, 2005, 2:07am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/27 "2005-02-06T02:07:51Z")
> [@Washoe](#): > > I see that the Italian study which mmmiiikkkeee referenced measured flaccid length, which is subject to far more variation than erect length. No it didn’t; you either found the wrong page or didn’t read the whole page. The study I referred to was American and tested all kinds of people - not just Americans. It measured erect, flaccid, head length, and girth to name a few, along with ethnic background, age, height, sexual preference, and so on. Type “the definitive penis survey” into Google, and it will be the very first in the list. They seem to be on their 6th edition right now. ---
**Author:** ![Washoe](https://avatars.discourse-cdn.com/v4/letter/w/ecae2f/32.png) [@Washoe](https://boards.straightdope.com/u/Washoe)\ **Post date:** [February 6, 2005, 9:27pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/28 "2005-02-06T21:27:45Z")
> [@mmmiiikkkeee](#): > > Type “the definitive penis survey” into Google, and it will be the very first in the list. I read the wrong page. The page you were trying to direct us to is called ‘the definitive penis size survey,’ not ‘the definitive penis survey.’ When I typed the latter into Google, it yielded six hits, the first of which was a breakdown of the Italian study which measured flaccid length. Even though this page was not consistent with what you described, I assumed that that was the page you were referencing, since there was no other available explanation. I later found the page you were really trying to send us to via alterego’s Wikipedia link. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [February 7, 2005, 7:17am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/29 "2005-02-07T07:17:43Z")
> [@threemae](#): > > Well, I’m damn sure that I’ve seen more than a few 10 inch plus penises. Are you sure? Think about it. 10" is about an inch longer than a can of Pledge, or a tad longer than a spray paint can with the cap on, or the distance from my wrist to the crook of my forearm. Hell, it’s 2" shorter than a 2 liter bottle! Or about an inch longer than a standard Kleenex box, etc… My point is, while you may have seen some truly gargantuan cranks in your day, 10" is probably a bit of an exaggeration. ---
**Author:** ![Go\_You\_Big\_Red\_Fire\_Engine](https://avatars.discourse-cdn.com/v4/letter/g/eada6e/32.png) [@Go\_You\_Big\_Red\_Fire\_Engine](https://boards.straightdope.com/u/Go_You_Big_Red_Fire_Engine)\ **Post date:** [February 7, 2005, 10:36am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/30 "2005-02-07T10:36:50Z")
Yeh, they seem a lot bigger till you measure them. And of course it depends on where you measure from. 6" can easily become 8". ---
**Author:** ![flight](https://avatars.discourse-cdn.com/v4/letter/f/bbce88/32.png) [@flight](https://boards.straightdope.com/u/flight)\ **Post date:** [February 7, 2005, 10:46am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/31 "2005-02-07T10:46:32Z")
> [@CynicalGabe](#): > > Its not the size of the boat, its the motion in the ocean… But it’s hard to sail to France in a dingy. ---
**Author:** ![aruvqan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aruvqan/32/2891_2.png) [@aruvqan](https://boards.straightdope.com/u/aruvqan)\ **Post date:** [February 7, 2005, 10:55am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/32 "2005-02-07T10:55:40Z")
> [@bump](#): > > Are you sure? Think about it. 10" is about an inch longer than a can of Pledge, or a tad longer than a spray paint can with the cap on, or the distance from my wrist to the crook of my forearm. Hell, it’s 2" shorter than a 2 liter bottle! Or about an inch longer than a standard Kleenex box, etc… > > My point is, while you may have seen some truly gargantuan cranks in your day, 10" is probably a bit of an exaggeration. I have dated a guy that was 9.75 inches measured hard from where the top of the penis meets the body, and a good solid 2 inches diameter base/1.75 inches diameter under the glans. I was _impressed_ but it seemed to fit…so females are a lot more ‘flexible’ in interior measurement. He wasn’t bad, he had the benefit of a first female lover who taught him that because he was so large he had to go carefully, and mot just emulate a battering ram. I have also dated a guy not quite as large but thought that the size/battering ram technique was the way to go and was a complete dud in bed pleasurewise for me at least. But then again I dated a guy that was tiny, barely 4 inches hard and 1.25 in diameter. He was excellent in bed - sort of like that avis commercial [we’re smaller so we try harder…] ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [February 7, 2005, 2:16pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/33 "2005-02-07T14:16:24Z")
> [@threemae](#): > > The point here being that normal distributions don’t seem to necessarily exist in real life. Of course, a normal distribution won’t apply here because it’s bounded on the low end by zero (I’m assuming that there are no negatives). Maybe the Rayleigh distribution would apply here. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [February 7, 2005, 2:21pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/34 "2005-02-07T14:21:35Z")
> [@CurtC](#): > > Of course, a normal distribution won’t apply here because it’s bounded on the low end by zero (I’m assuming that there are no negatives). Maybe the Rayleigh distribution would apply here. Well, there is that other half of the population… ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [February 7, 2005, 2:25pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/35 "2005-02-07T14:25:57Z")
> [@Go You Big Red Fire Engine](#): > > Yeh, they seem a lot bigger till you measure them. And of course it depends on where you measure from. 6" can easily become 8". I prefer to lay down on my back on the bed, take out a tape measure, start it on the mattress while pushing down on the mattress as hard as I can and measuring up to the tip of my penis. I would have never have guessed that I was 13 inches but I have proof now. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [February 7, 2005, 2:30pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/36 "2005-02-07T14:30:58Z")
> [@flight](#): > > But it’s hard to sail to France in a dingy. Wait, I thought the “little man in the boat” was… 😕 ---
**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:** [February 7, 2005, 10:35pm UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/37 "2005-02-07T22:35:28Z")
> [@](#): > > Well, there is that other half of the population… Which would give the distribution a distinctly bimodal character, which is even less Gaussian. Or we can just accept that zero is far enough out in the tail to disregard, and call the distribution for males approximately Gaussian. The Gaussian distribution isn’t “normal” because it’s truly common; it’s normal because it’s a good approximation to many true distributions. ---
**Author:** ![DiosaBellissima](https://avatars.discourse-cdn.com/v4/letter/d/a8b319/32.png) [@DiosaBellissima](https://boards.straightdope.com/u/DiosaBellissima)\ **Post date:** [February 8, 2005, 3:57am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/38 "2005-02-08T03:57:02Z")
> [@CynicalGabe](#): > > Its not the size of the boat, its the motion in the ocean… I have a theory that females only say that to guys with small penises. ---
**Author:** ![bbs2k](https://avatars.discourse-cdn.com/v4/letter/b/e495f1/32.png) [@bbs2k](https://boards.straightdope.com/u/bbs2k)\ **Post date:** [February 8, 2005, 8:18am UTC](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334/39 "2005-02-08T08:18:50Z")
When measuring penis length I always use the Adam Carolla technique. Which is to start measuring from the anus, follow this underneath the shaft, and stop measuring approximately 4 inches past the head. Now you can brag openly about your 8-inch penis. [Previous page](https://boards.straightdope.com/t/what-is-the-standard-deviation-of-penis-size/288334.md?page=1)