The area of each rectangle in a view window is proportional to the size of the file it represents. There is, however, more than one way to measure a file's size. GrandPerspective therefore supports two different file size measures:
By default, GrandPerspective reports logical file sizes. You can change the file size measure that is used by changing the application's Preferences. The change comes into effect when new folders are scanned. It does not affect existing views, or views that are created after re-scanning (as the latter take their settings from their original view).