As the carcels say, aint no replacement for displacement so surely this applies to penors as well.

I ran the math but maybe some our resident math doctors can check my work.

Penor Displacement = (Length * Girth^2) / 4pi

or if you don't like pi:

Penor Displacement = (Length * Girth^2) / 12.56

Now I've approximated the penor as a cylinder so that's average girth not max girth for you tapercels or baseball bat dinks

Using this formula on my healthy 8x5 comes out as a Penor Displacement of 15.92 cubic inches.

Anyone else want to share their Penor Displacement? Who can beat my 16 cubes?