On the bottom left of your screen practically on the window after you save there's a few little boxes one typically says 100%. Next to it on the right or left depending on version after you save it shows you the byte size of your file, or if your in a version that doesn't have it, you can tap down the byte size of free space available before you save, and then subtract after you save.
Or you can just look at file details in windows.
If your looking for the conversion between inches and pixels. I believe for Illustrator exports 115 pixels = 1"
