As per Wikipedia,

As of 2015, a systematic review of 15,521 men, who were measured by health professionals rather than themselves, concluded that the average length of an erect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches).

First, find the radius of a circle per the formula C=2πr. The radius of an average human penis is ≈1.86 cm.

Second, to find the volume of the cylinder in question (the penis), use the formula V=πr2h, plugging in the radius and length. The volume of an average human penis then comes out to ≈142.59674 cm

^{3}.

I assume if the penis were liquified the volume would not change. I know the volume for a flaccid penis would be different but, let's be honest, if I'm going to stick my dick into a Baby Bullet and turn it up to high, I am obviously already going to be engorged and throbbing. Please correct me if I'm wrong, I'm interested in advancing scientific curiosity and, in addition, bottom surgery is pretty expensive.