I've heard that muscle is about 4x the weight of fat. So you could reason, the square unit of fat would be 4 x larger then the square unit of fat. If that even makes any sense heh.
No specific numbers, but here are some facts I dug up:
"Muscle is much more dense than fat (hence, one pound of muscle, while weighing the same as one pound of fat, occupies much less space). Muscle tissue is approximately 70 percent water; conversely fat is less than 25 percent water. A pound of muscle contains under 700 calories whereas a pound of fat will yield 3500 calories. In addition a pound of muscle is approximately 18 percent smaller by volume than a pound of fat."
Also, here's a link to an old thread from right here on Elite - the last person to post claims that five pounds of fat takes up the same volume as a shoebox (not sure where he got that...):