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Interesting -- Average Size Chart


Interesting -- Average Size Chart

This shows the mean stretched length is 5.2 inches for an adult … ????

Normal Penis Size
Provided by
Q: How can I tell if my baby’s penis is the normal size for his age?

A: In determining size, the “stretched penile length” is far more important than the “relaxed length.” To evaluate penis size, stretch the penis gently and measure from the bone at the base all the way to the tip. Be sure to depress the surrounding fat pad to get all the way to the base. Here are the normal values:
Average Stretched Penile Length

(Adapted from Feldman KW, Smith DW. Journal of Pediatrics. 1975; 86:395):

Age Mean +/- 1 SD (inches) Mean - 2.5 SD (inches)
0-5 months 1.5 +/- 0.3 0.75
6-12 months 1.7 +/- 0.3 0.9
1-2 years 1.9 +/- 0.3 1.0
2-3 years 2.0 +/- 0.4 1.1
3-4 years 2.2 +/- 0.4 1.3
4-5 years 2.2 +/- 0.4 1.4
5-8 years 2.4 +/- 0.4 1.5
8-11 years 2.5 +/- 0.4 1.5
Adult 5.2 +/- 0.6 3.7

Last Reviewed: October 2002 by Khanh-Van Le-Bucklin, MD

By the way, what is a standard deviation?

Standard deviation is a measure of how widely values are dispersed from the average value (the mean).

Example when used in Microsoft Excel:
Suppose 10 tools stamped from the same machine during a production run are collected as a random sample and measured for breaking strength. The sample values (1345, 1301, 1368, 1322, 1310, 1370, 1318, 1350, 1303, 1299) are stored in A2:E3, respectively. STDEV estimates the standard deviation of breaking strengths for all the tools.

STDEV(A2:E3) equals 27.46

And yeah, 5.2 FSL is way too low of a number.

Originally posted by beowulf
By the way, what is a standard deviation?

Say for example you take 5 samples of penis size and get

The average of this is 6.1 inches. The standard deviation would be the average of the distance from the average to min and max. For example in this situation, the max is 7.9. 7.9-6.1 = 1.8. The Min is 5.1. 6.1-5.1=1.0. So the standard deviation is 1.0+1.8/2 or 1.4”. So it says that on average, a penis is 6.1”, and usually people fall within the range of 4.7”-7.5”. With a larger sample size, this gets more accurate, but generally it is correct. (Of course I think SD is deviation from the mean rather than the average, but you get the idea)

Starting: 5.75" EBPL x 5" EG 10/10/03 Current: 6" EBPL x 5" EG 11/6/03 Goal: 8" EBPL x 6" EG

I think I get the idea. Does this SD have to do with percentages as well? And Stevie, I hope my tool doesn’t break!

Esac … I was just looking at Stevie’s #’s and tried to duplicate his excel results with your formula. It didn’t work. I came up with an average of 1328.6 and SD of 35.5. This doesn’t make sense. Even your example doesn’t make sense because 4.7 as a low end deviation is smaller than any in the sample size. What am I missing?

I got 1.095 SD for esac’s numbers using Excel’s STDEV function:

Here is the first hit on Google.

Regarding the value of 4.7: I’ll talk about two things here. One is appropriate data, the other is appropriate use of statistics.

DATA - What you’re missing is that standard deviation is an almost worthless metric unless you meet the following criteria…

1) Sufficiently large sample size. And this size is highly variable depending on many factors.

2) An average value “appropriately” close to both the max and min values.
i.e. the average for ALL values should be “somewhat near” the average of just the max and min.

3) The measurments should roughly approximate a gaussian (or similar) distribution. You know this as a “bell curve”.

So, like almost all statistics, S.D. is an “ideal” calculation. The closer your data are to approximating this ideal, the more relevant the notion of a standard deviation becomes. But if your data violate one or more of the previous three rules by too wide a margin, then S.D. is just some number which doesn’t mean anything. You can calculate it, but what for?

So go back to the example and look. I’m assuming esac chose his data randomly, so we can ruthlessly bash the results. :-)

1) There are only 5 data points, which is so few as to produce meaningless, almost random results. He just wanted to show you how to do the calculations.

2) The distance from max to average is 1.8, the distance from min to average is 1.0. That’s an aweful large spread. It’s a hint that we’re violating rule three…

3) Look at the data again. How do you construct a Gaussian distribution from that? You can’t. You can’t even get close. There are other curves that you can use, but they have different and more complicated distribution formulas. They’re a perfect pain in the ass to work with, also.

STATISTICAL USAGE - One other point to keep in mind is that esac could have given us a much larger and better dataset, and still come up with the same problem. Namely that 4.7 would be smaller than any datapoint we have.

This is perfectly reasonable. The purpose of a standard distribution is either to validate a theory (by showing that the actual S.D. reproduces our expected outcome) OR to provide a tool for prediction. That second part is important.

So maybe 4.7 is lower than any of our actual data. That’s ok because what it really means is that “if we select one more person at random and take their measurement, we expect them to fall within a certain range.”

Would it surprise you to find someone with a penis less than 5.1 inches? Of course not. Just because you haven’t seen one yet doesn’t mean you don’t ever expect to see one!

Example: Your dad is 6’2”, you are 6’0”, and you have a brother who is 6’3”. If another brother is born, would you assume that he must grow to be between 6’0” and 6’3”?

And finally, note that esac only showed 1 S.D. This is where we expect to find about 85% of a population. He could have extended his estimate to 2 or 3 S.D., which is where you expect to find ~95% and ~99% of a population, respectively.

Hope this helps,

busted bus

bb, why have I thought that 68% fall within 1 SD of the mean for a normal distribution?

Please :donatecar to Thunder's Place to keep it running.

Originally posted by bustedbus

So go back to the example and look. I'm assuming esac chose his data randomly, so we can ruthlessly bash the results. :-)

Yeah I chose the data randomly so bash away, my point was just to help him get an idea on how an SD is determined without getting TOO mathematical as I don’t know his background.

Starting: 5.75" EBPL x 5" EG 10/10/03 Current: 6" EBPL x 5" EG 11/6/03 Goal: 8" EBPL x 6" EG

Bustedbus, good stuff as usual.

I wish you would have taught my stats class. :)

Hey Stud,

I’ll tell ya why you thought 68%. Because I’m wrong, that’s why! ;-)

You’re right that 68% fall within +/- 1S.D. of the mean.

What I should have said is that 85% fall UNDER +1 S.D. Similarly, 95% fall under +2 S.D. and 99% fall under +3 S.D.

busted bus

Cool. I was only asking because I know you know a hell of a lot more about a stats than I do, and I thought maybe I didn’t undersatnd something. Was not trying to point out your typo or whatever!!

Thanks for all the useful info again.

Please :donatecar to Thunder's Place to keep it running.


That’s no prob at all. Someone’s gotta keep me honest!

busted bus

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