FolderSizes contains broad support for computing and displaying both actual and allocated file sizes. Allocated sizes are also sometimes referred to as "size on disk".
Allocated size columns are displayed by default within the main window detail view, file report detail views, and search result detail views. They can also be shown within graphs (see related graph option).
What Exactly is Allocated Size?
In FolderSizes, allocated file system object sizes are influenced by a number of factors.
1.Cluster overhang - Windows allocates space to files in units called clusters. Any file with a size which is not an exact multiple of the file system's cluster size will consume more space on disk than it's actual size.
2.NTFS compression - NTFS supports a built-in compression mechanism that can reduce file sizes significantly.
3.Sparse files - Sparse files allow the Windows operating system to use file system space more efficiently when blocks allocated to the file are mostly empty.
4.Hard links - NTFS hard links allow multiple file allocation table entries to resolve to the same file. When hard link tracking is turned on, files with multiple hard links will affect allocated file size (allocated size is divided by the number of links).
Each of these factors (in combination) is evaluated during the computation of allocated space within FolderSizes.