Can Photoshop figure out the square footage of an element in a layer or a selection. It's the only element in the document. It's just not the whole canvas (there's transparency) and it's not a square or rectangular shape?
Photoshop can tell you how many pixels are in the selection -- but how that relates to length and area depends on how you set the scale of the document.
From the number of pixels, you can determine the area.
With measurements in Photoshop, you can do that automatically once you have set the scale correctly.