Average Penis Length Changes From Flaccid to Erect

Some men’s penises seem to grow more than others when they change from a flaccid to erect state. In colloquial terms, men who experience a larger increase in length are often referred to as “growers”; by contrast, those who have a smaller length increase are often referred to as “showers.”
So what is the typical change in penis length from flaccid to erect—and just how many men fall into the category of grower versus shower anyway? A recent study published in the International Journal of Impotence Research offers some insight.
In this study, 274 men had clinical measurements performed on their penises at two different points in time: once while in the flaccid state and again while at peak erection following injection of a vasodilator (i.e., a substance that chemically causes an erection). Note that all men in this study were actually undergoing clinical testing for erectile dysfunction, hence why the vasodilator was administered.
The median change in penis length (i.e., the 50th percentile) was 4 centimeters (about 1.6 inches). The researchers categorized men who grew by more than this as “growers” and those who grew by less as “showers.”
It turned out that far more men were showers (74%) than growers (26%). On average, the showers increased by 3.1 cm (1.2 inches), whereas the growers increased by 5.3 cm (2.1 inches). Men who were younger were more likely to be growers.
It’s important to note that we’re not dealing with representative data here (especially considering that all of the men were undergoing testing for ED), so we should be cautious about generalizing the results. As always, more data would be necessary to draw, ahem, firm conclusions—however, these findings suggest that the average change in penis length from flaccid to erect seems to be between 1-2 inches and, further, that being a shower may be more common than being a grower.
Want to learn more about Sex and Psychology ? Click here for previous articles or follow the blog on Facebook (facebook.com/psychologyofsex), Twitter (@JustinLehmiller), or Reddit (reddit.com/r/psychologyofsex) to receive updates.

August 31, 2018
To learn more about this research, see: Yafi, F. A., Alzweri, L., McCaslin, I. R., Libby, R. P., Sangkum, P., Sikka, S. C., & Hellstrom, W. J. (201. Grower or shower? Predictors of change in penile length from the flaccid to erect state. International Journal of Impotence Research.