What is the average density of the human body?

Well, it's just about the same as that of water, because when you
put the average human being in water, he just barely floats in it.
Some people (me, for example) can sink or float depending on how much
air they hold in their lungs, so their density can vary from just
below to just above 1.0 g/cm^3.
Human body density is 61 to 67 pounds per cubic foot. Most people use 64 pounds per cubic foot because it equals 8 squared and 4 cubed.
Water weighs 62.42796 pounds per cubic foot.