Average Length of a Penis
Penises come in a wide variety of lengths, from the very small to the very long, but most guys fall pretty close to the average (obviously).
Porn has warped a lot of men's ideas about what the average penis looks like, but especially how long the average penis is. Most men that you see in porn are outliers, sometimes extreme outliers. The truth is, the average penis length is much more modest.
With that said, lets get to the average penis length.
Average Length of an Erect Penis
Penis lengths are measured in two ways, flaccid and erect, but lets face it, most guys (and their partners) only really care how long a penis is when it's erect. Doubly so for those of us who are growers, not showers!
A 2015 study looked at data from over 15,000 men, and found that the average penis length is 5.16 inches (13.12 cm).
For reference, a US dollar bill is 6.14 inches long. So the average penis is about an inch shorter than a dollar bill, or 5/6 of a dollar bill. A roll of toilet paper is 4.5 inches long. This givees you a few convenient things to measure yourself against :)
Average penis length graph, reproduced from this study.
Average Length of a Flaccid Penis
Probably of less interest to you, but the study in the references section below also found that the average flaccid penis length is 3.61 inches (9.16 cm).
They also found that the average penis length when flaccid and stretched is 5.21 inches (13.24 cm).
Why stretch a flaccid penis and then measure it? Well readers paying attention may have noticed that the average flaccid streched length of a penis (5.21 inches) is very close to the average erect length of a penis (5.16 inches). These two numbers are very close together and so are highly correlated. If you know how long your penis is while flaccid and streched, that's a pretty good indicator of how long it will be when erect. Penis science!
Penis Length Standard Deviation
Standard deviation is helpful for figuring out where your penis length fits, within the range of all the other guys out there. The graph above can be used to figure out approximately what percentile you're at (you can also check out our penis score calculator to get more in-depth).
The researchers in the meta-study linked to below found that for erect penis length, the standard deviation was 0.65 inches (1.66 cm). That means that about 68% of the population has an erect penis length somewhere between 4.51 inches (11.45 cm) and 5.81 inches (14.76 cm) in length.
And for the flaccid penises out there, the standard deviation of the length is 0.62 inches (1.57 cm). That means that 68% of the men out there have a flaccid penis length of somewhere between 4.59 inches (11.66 cm) and 5.83 inches (14.81 cm).
Last but not least (because they're actually the longest) are the stretched flaccid penises. There, penis length standard deviation comes out to 0.74 inches (1.89 cm). So 68% of men's flaccid, streched penises are between 4.47 inches (11.35 cm) and 5.95 inches (15.11 cm) long.