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I am trying to clean up some free space on my SSD C: drive, and I am getting some inconsistent information depending on the tool I use to look at drive usage.

If I look at the drive through file explorer, I see the drive is 232GB, with 112GB free (120GB Used).

If I look at disk usage through windirstat (run as admin to see all files) it reports 106.5GB of files on the drive, so (125.5GB free).

If I go into the c: drive, and select all files (Hidden and System files, page file, hybernate/etc), it shows 94.8GB of files 93.2GB on disk (I have a few compressed directories), meaning there should be 137.2GB of free space.

All told thats a 25GB difference in free space depending on where I look. I checked for system snapshots using vssadmin list shadowstorage, and it is showing 0 usage. I emptied my recyclebin. I am not sure what else could be using the space. I've got plenty of free space on the drive now, but a missing 10% is driving me nuts.

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The file size is not the same as the space used on the disk.
The default cluster size on NTFS is 4kB so the space used by every file should at least be rounded up to the next 4kB. Also the space for directory entries are rounded up to 4kB.

For one of my directory I see from Explorer

File Size   303 MB (318.602.178 Bytes)   
Space Used  358 MB (375.513.088 Bytes)

33.188 Files, 1.859 Folders

The extra space in this case is ~ 18%.

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  • I don't think that really addresses my question. I understand the difference between file size, and the amount of disk space required to actually store said file. If I select all files and folders on my c: drive, I am only getting 93.2GB for the file size on disk, meanwhile windows file explorer reports that I am using 120GB of space on the drive.
    – Patrick
    Commented Dec 30, 2018 at 3:22
  • Have you considered the system hidden files and directories ? Windirstat give the files size not the space used, and it agrees with explorer to the byte on my W10.
    – matzeri
    Commented Dec 30, 2018 at 5:16
  • I have explorer set to show hidden and system files. I confirmed that I am seeing hidden directories, and system files by navigating into appdata directories (normally hidden), and confirming that I see the pagefile and hibernate files at the root of the C:\ drive.
    – Patrick
    Commented Dec 31, 2018 at 13:18

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