What percent of the human body is penis?

Human body volume is approximately equal in L to the weight in kg (see: the internet)

e.g. a 180 lb male would be about 80kg, which is roughly equivalent to 80 L

Now, we need a little math for the 2nd part: penile volume

Recall the volume of a cylinder is equivalent to the area of a circle multiplied by the height, or

V = (pi)r2h

We can estimate area from circumference: 2(pi)r. If the average human penis girth (circumference) is about 12cm, that means the radius would be somewhere around 2 (12 / 2 / pi).

The average length (height) of the penis is about 15 cm, so with all of that, we have:

V = pi * (2)2 * 15 = ~190 cm3

Now, we simply divide this by the original volume (80 L, or 80,000 cm3):

190 / 80,000 = .002375, or .2%