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I'm thinking of installing an SSD on my machine at home, and the easiest way to do this is basically to clone my current hard drive over to the new SSD. Trouble is, if I right click on my current hard drive and select properties, my used space is 230GB, thus requiring me to buy a monster SSD.

However, if I right click on each of the top level folders in my hard drive and select properties, the total space used by those folders is only 140GB. 100GB of that is music and movies, which I can easily clean out before the move to the SSD.

So here's the rub, where did the other 90GB go? For the life of me I can't figure it out. Shouldn't the sum of the used sizes of all the top level folders in your C: drive roughly equal the used size of the C: drive itself?

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    This may not be a directly addressed to your question but in buying a SSD it may not be necessary to get one which has comparable storage capacity as your current HDD. If it's speed (of read and write) your after it might suffice to buy a SSD of less storage capacity, say 80 GB (they seem to be reasonably priced now), and on it your put the system files (the OS and the programs) aswell as the files your currently working on. Then you just store whatever other files your not currently working on, or don't need hasty read and write for (these could be media files), on your current HDD.
    – N.N.
    Jun 30, 2011 at 13:16
  • Everything you've said is true. Unfortunately, I couldn't figure out a way to easily move Windows without formatting my current drive, and I can't find the DVDs for half the stuff I have installed. I know I know, that's my fault, but just doing the image will the whole process go so much smoother.
    – WindyCityEagle
    Jul 1, 2011 at 2:43
  • Keep in mind that the size of each file is quite different than the space it takes on disk. Uncompressed files take more space on disk than they actually are in length, compressed files can take less.
    – Mooing Duck
    Apr 12, 2013 at 0:43
  • 2
    possible duplicate of What is the difference between "used space", "size" and "size on disk"?
    – DavidPostill ♦
    Dec 7, 2014 at 21:44

11 Answers 11

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There are hidden files and directories which contain system files that are not included in the calculation. System volume information, for example, contains your system restore points and volume shadow copies among other things. It is not included in the calculation because by default the ACL does not allow your user account to view the folder or it's properties. You can gain access to it if you really want to, however.

On another note, the cleanmgr.exe utility (better known as Disk Cleanup) can help you reclaim most of your disk space. The More Options tab allows you to delete all but the most recent restore points and Volume Shadow Copies.

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  • Ahhh, More Options. That's what I was missing. I hadn't figured out the secret Windows 7 trick to make the more options tab appear. Turns out I had 90GB of System Restore data.
    – WindyCityEagle
    Jul 1, 2011 at 2:41
  • If you can identify that the problem is the size of the "System Volume Information" folder, right-click on the Volume and see if there is an option for "Configure Shadow Copies...". If so, open it, select the desired volume and click settings to see if there is a Maximum Size set, or if it's too big. If you decrease the maximum size and click OK, you should see the volume use start to decrease.
    – Geoff
    Jul 20, 2020 at 20:15
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Use WinDirStat to see where your files are taking up space:

http://windirstat.info/

It is free, lightweight, and there is no easier way to see your usage by directory.

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  • Thank you. This is a great utility app. I was using Folder Size which is good, but it skips some files.
    – Hong
    Jan 12, 2015 at 15:50
  • This is exactly what I was looking for
    – Kerry Jones
    May 23, 2015 at 11:38
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    I used WinDirStat and it reports 350GB in the program, but Windows shows 1.5TB used, so this might not be the solution for all.
    – Swisher Sweet
    Feb 26, 2017 at 0:13
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    I recently found out, you should run WinDirStat (or similar pieces of software) as Administrator in order for the program to correctly find and sum up all files/dirs (especially files in the Windows-folder, that are otherwise skipped). Simply right-click executable and select "Run as administrator"
    – Frederik Struck-Schøning
    Jul 31, 2017 at 8:55
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Here's a comprehensive list of all the reasons I can think of why the used space in a hard drive may be greater than the sum of the file sizes. OP has already solved his/her problem, but the issue may remain for some lurkers.

  • A file takes up more space on the disk than merely its size. For example, a text file that contains the letters "hello" has a file size of 5 bytes, but it also takes up space in the filesystem's table to store its name and properties. Usually the difference is not greater than a few hundred bytes, but if you have many tiny files, that can add up to quite a bit. You can see the difference by comparing "Size" and "Size on disk" numbers after opening the properties dialog of a file in Windows' file explorer.
  • You may be forgetting to check hidden files: make sure you have "show hidden files, folders and drives" enabled in Windows' file explorer options.
  • You may be forgetting to check system files: make sure you have "hide protected operating system files" disabled.
  • You may be forgetting to count the recycle bin which is a special case of hidden and system files.
  • Contents indexing takes up space: if you open the properties dialog for a partition, you can see the option "Allow files on this drive to have contents indexed in addition to file properties". This takes up space, I'm not quite sure where on the file system.
  • Previous versions (or shadow copies or file history) take up space: NTFS has the feature of shadow copies of files, which takes up space not counted in the plain file size.
  • You may have enabled compression: this should theoretically cause the used disk space to be smaller than the sum of the file sizes, rather than bigger, but in any case, it's a spanner in the works. You can check by opening the properties dialog of a partition in Windows' file explorer.

Also, remember that you may have hidden partitions, or unallocated space on your hard disk where you could have a partition. Open "Disk Management" shipped with Windows to check this.

If anything is missing, go ahead and edit my answer to make this as comprehensive as possible. I'm happy to make this a community wiki post.

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I recently had the same question, but I stumbled upon the answer. Symantec Norton was scheduled to periodically backup files by storing them on my hard drive. I found the folder containing the backed up files and discovered that these backed up files added more than 100 GB to the quantity of data stored on my hard drive. Because I frequently back up my modified files and folders onto removable hard drives, flash drives, etc., I do not need the Norton backup utility. I simply deleted the files and canceled future Norton backups. The resulting increase in space on my hard drive was enormous.

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My problem was with Windows/Temp.

The contents are only visible if you are in admin mode evidently. So simply asking it how much space the Windows folder was taking up did not show the amount taken by the Temp folder. When I asked to delete it I got the admin popup that I just approved and it erased it.

The WinDirStat utility recommended above by KCotreau found this for me.

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  • I had exactly the same problem. 66GB hidden in Windows/Temp, which was only visible after the first attempt to access and confirmation. Thanks a lot. There really should be a list of such places.
    – iavr
    Sep 22, 2018 at 15:02
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Hidden swap file/directory (recycling bin?) in the root directory?

Also does the windows explorer in win7 consider hidden files inside those directories when tallying it's total?

Just a couple guesses.

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In may case it was the page file dll that occupied around 6GB and the hibernet.dll file that occupied around 2GB.

If you enable "Show protected operating system files" then you can see those two files.

You cannot and should not directly delete the files. If you really need some space and want to remove the files please google for the proper procedure.

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Hiberfil, Hidden files, Temp folder, System protection files, a few MBs here a few KBs there! Too many places to check and the total space still won't add up. Even if you delete them all, you'll free only a few gigs, and I have about 100GB missing!

Run the software as admin folks!

Whichever software you are using to show your disk space, run it as administrator, or otherwise it just can't show you everything.

I tried SpaceMonger, WinDirStat, etc. but none could show the messy 97GB SQL log file unless I run them with elevated privilege.

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To know the exact memory allocations in the drive, open "storage" using bottom-left search pane and click on the drive you want to examine.

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  • I don’t know what you’re talking about.    Can you provide clearer instructions and/or a screenshot?
    – Scott - Слава Україні
    Feb 7, 2019 at 4:12
  • The question asks why. This doesn't answer that.
    – fixer1234
    Jul 27, 2019 at 4:39
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Use this software. It gives you the exact size. https://www.jam-software.com/treesize_free/

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I had the same issue, the files on a 4TB hard drive only added up to 2.9TB but Windows reported it was full. Today I had a power outage and the 1TB is suddenly back! I think the computer ran a disk checking on startup and fixed an incorrect sector count, but I'm not an expert on how this works. Try using Treesize or Windirstat, and if that doesn't show the same amount of usage as Windows itself does, maybe there is some corruption in your master file table. I suggest trying to run chkdsk, I don't remember the command for doing it next restart, but you can use Google for that. On Mac, you can use disk aid in disk utility.

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