Windows always slows down a lot when free space on the system drive (the drive or partition Windows is installed on) falls below 10% of total disk space. So keep at least 10 GB free on a 100 GB system drive, but no matter how small your drive is, do not let free space on your hard disk drop below 2 gigabytes to ensure there is enough free space available for updates and temporary files.
When available disk space on the system drive falls below 5%, some functions in different programs might stop working properly - for example, Google Chrome will fail to update to a newer version.
In case Windows is unable to boot due to insufficient disk space, use a bootable USB drive or CD/DVD, such as Puppy Linux to start your PC properly and move your largest personal files to an external drive to free up at least 1 GB of disk space on the system drive (the one where Windows is installed).
In Windows 10 Anniversary Update and newer, open the Run dialog with keyboard shortcut Windows Key+R or via the Quick Links menu (Windows Key+X), type ms-settings:storagesense, and click OK. This will open the Settings app with an overview of drive space usage.
In all Windows versions, open (My) Computer or This PC from Desktop or Start menu/screen, or use the keyboard shortcut Windows Key+E.
If you have this folder in Details, Tiles, or Content view, you can just check what's written in the Free Space column of hard disk with Windows on it (usually Local Disk (C:) or Local Disk (D:)).
In Windows Vista, 7, 8/8.1 and 10, a good indication of disk space usage is also the Space used progress bar - if the bar is blue, you have more than 10% of free space on the drive; if the bar is red, you should free up some space on the disk.
In Windows Vista and 7, you can also click on a disk once and see Space free and Total space values in Details Pane in the lower part of the window. The Space used bar is also here to indicate the level of disk usage.
In Windows XP, right-click a disk and select Properties from the menu.
Then see what's written in the Free Space row.
To see disk space usage analysis in Windows 10, open the Settings app (keyboard shortcut Windows Key+I) and navigate to System, Storage tab.
Alternatively, in Windows 10 Anniversary Update and newer, open the Run dialog with keyboard shortcut Windows Key+R or via the Quick Links menu (Windows Key+X), type ms-settings:storagesense and click OK.
First, if your device has limited total disk space (less than 200 GB), you might want to change the default save locations for new apps, documents, music, photos, videos, and offline maps by clicking or tapping the Change where new content is saved link in the More storage settings section of Storage tab.
You can choose to store these on an SD card, or on USB sticks and internal or external hard drives.
Do note that this setting affects new items only!
Please note that storing apps on a slow SD card (Class 6 and lower) can negatively impact app performance. At least Class 10 media is recommended.
To move existing third-party apps to another drive, click or touch Home in the Settings app first, then open Apps. As expected, Microsoft does not allow moving its apps to an alternate location, so only third-party Windows Store apps can be moved. You also cannot move traditional desktop programs - but many of these allow choosing destination drive and folder during installation.
Click or touch an app in the list, then hit the Move button (if available) and choose the destination drive.
To check what's using space on a drive, click or tap the drive in the Storage section.
Windows 10 will first refresh storage usage analysis for the selected drive, this might take several minutes to complete. You can later refresh the stats manually with the round arrow button next to the "Last refreshed on" line.
The analysis is divided into sections, such as System & reserved, Apps & features, Documents, Pictures, Other people, etc. Click or touch a section to see more detailed usage counters and possible solutions.
The sections are sorted by size, larger ones on top.
The System & reserved section allows managing the Hibernation file and System Restore options. Please note that the latter is turned off by default in Windows 10. You will usually not free much space in this section unless you want to risk deleting all but the latest System Restore point (not recommended).
The Apps & features section shows which Windows Store (aka Modern UI/Metro) apps and desktop programs use the most disk space. To begin, you should sort the results by size.
To modify or remove an app/program, click or touch it in the list and choose the option you need. Please note that you can also move some Windows Store apps to an SD card or an external drive.
Documents, Pictures, Music, Videos, and Desktop sections open the respective folders in File Explorer so that you can manually remove the items you do not need anymore. To prevent accidental data loss while cleaning up these folders, make sure that File History has been turned on for your account, and that it does have a recent backup.
The Maps section opens the settings of the offline maps where you can delete the data or move it to external storage.
The same applies to the Mail section.
The Other people section has a link to managing user accounts in the Settings app but it displays how much disk space other people are using.
The OneDrive section contains dropdown(s) for choosing the number of days (Never, 1, 14, 30, or 60) before unused files are deleted from your device (the files still remain on your OneDrive and will be downloaded again if you open them). Users with paid plans might recover quite a bit of space by disabling sync selectively.
Do note that you need to have the Save space and download files as you use them option turned on in order to see OneDrive listed here - instructions are provided below. If you have multiple OneDrives connected (for example, your personal one and your company's OneDrive for Business), you need to enable the option for each one separately.
The Files On-Demand option is available for OneDrive since Windows 10 Fall Creators Update (October 2017): files are kept in the cloud and downloaded only if you open them. This might be extremely useful on devices with limited disk space.
To enable the feature and free up disk space, right-click or tap and hold on the OneDrive icon in the Taskbar Notification area, choose Help & Settings and click Settings. Then, in the Settings tab, Files On-Demand section, tick the Save space and download files as you use them checkbox.
Then go to File Explorer (keyboard shortcut Windows Key+E) and navigate to your OneDrive folder. All files and folders with the green circled checkmark in the Status column are kept on your device for offline access. Right-click or tap and hold a file or a folder and choose the Free up space command to enable the Files On-Demand feature for this item and reclaim some disk space. Now the items are available only when the Internet connection is working properly.
For extremely important items, you might want to choose the Always keep on this device command instead.
In the Temporary files section, you can view (the original Windows 10) or empty (Windows 10 Anniversary Update) your Downloads folder, clear Recycle bin and temporary files, and delete installation files for the previous version of Windows. Please note that using the last option will also disable version rollback in Settings, Update & Security, Recovery.
In Windows 10 Anniversary Update and later, you can use checkboxes to select items and click or touch Remove files. In the original Windows 10, you need to click or tap a button for each item separately. Please wait until the process completes, navigating away from the section will cancel it.
Each newer Windows 10 feature update adds more options to the Temporary files section, and safe-to-remove ones have been selected automatically.
Finally, the Other section contains uncategorized folders. Choosing an item here opens it in File Explorer for manual checking and/or cleaning.
In this example, the ESD folder is leftover from creating Windows 10 installation media and it is safe to remove. If you have no idea why a folder is on this list, please do not delete it: instead, move it to an external drive, restart your device, launch your favorite apps and verify there are no error messages for missing files. A week or so without errors means that you can safely clear the folder on the external drive.
Storage sense in Windows 10 Creators Update and newer
Windows 10 Creators Update (April 2017) introduced the Storage sense feature that automatically removes older Recycle Bin files and temporary files. This is a good idea for those who have constant problems with available disk space. At first, Storage sense only ran automatically when a device was nearly out of disk space, but the April 2018 Update added options for more control over automatic disk cleaning.
To take advantage of Storage sense, set its slider to On. This is very much recommended.
Please note that Storage sense is a per-account setting: each user can turn it on or off and can configure its options differently.
To perform the cleanup right away, or to configure Storage sense settings, click or touch the Change how we free up space link.
The two configuration options in 2017 feature updates of Windows 10 - Delete temporary files that my apps aren't using and Delete files that have been in the recycle bin for over 30 days - are pretty self-explanatory.
Windows 10 Fall Creators Update (October 2017) added the Delete files in the Downloads folder that haven't changed in 30 days option - use this one with care, especially if you tend to keep downloaded files indefinitely. Luckily, its default state is disabled.
Windows 10 April 2018 Update added the Run Storage sense dropdown that lets you choose when Windows should do the automatic cleanup. By default, it only runs when Windows decides (during low disk space), but you can set it to do its job Every day, Every week (my recommended setting), or Every month.
To emphasize that Storage sense configuration affects the currently signed in account only, the two options are now called Delete files in my recycle bin if they have been there over and Delete files in my Downloads folder if they have been there over - both can be set to Never, 1 day, 14 days, 30 days or 60 days.
By default, files in your Downloads folder are not deleted, and files that are more than 30 days old are removed from Recycle Bin.
If you recently upgraded Windows 10 to a newer version, there is also the Delete previous versions of Windows checkbox available. This one should be ticked only if your device is in really-really desperate need of disk space right now.
Please note that Windows 10 removes older installations automatically after 10 days, so most users should not really worry about this option.
To run the cleanup right away, click the Clean now button in the Free up space now section. A checkmark appears next to the button after the process is complete, and you can also see the amount of gained disk space above the button.
If you still need to reclaim even more disk space, jump to the Using Disk Cleanup for deleting temporary files in Windows section.
Windows 8.1 Update 1 has the Disk space and App sizes options in its PC Settings app. To access these, open the Start screen, type disk, and click Free up space on this PC.
Wait for a few minutes until Windows 8.1 grinds your hard drive and calculates the totals.
The first progress bar shows the total available space on your system drive (the drive where Windows 8.1 is installed).
Apps, Media and files and Recycle Bin sections concern only the currently logged on user account (this means your account) only. So yeah, if you have multiple user accounts on the PC, tell the other users to clean up their chunk of disk space, too.
The first step is normally clicking the Empty my Recycle Bin button at the bottom.
Then see which items consume the most storage space in the Media and files section. In this example, the Downloads folder is abnormally large and you should probably clean it up.
Finally, click the See my app sizes link in the Apps section. Usually, games are the most space-hungry items among Windows Store (aka Modern UI or Metro) apps, but you can always uninstall the applications you do not need or use.
Here's an example of App sizes. To remove an oversized or unneeded app, click or tap it in the list and then use the Uninstall button. Note that the total available disk space is displayed here, too.
Click or touch to select the system drive (the drive where Windows is installed) in Windows/File Explorer, then right-click or tap and hold the drive and choose Properties. In Windows XP, you can just right-click the drive; in newer Windows versions you must select it first.
Make sure the General tab is open. Click Disk Cleanup.
Windows Vista will ask whether you want to clean up just your own files or files of all users on the computer. Click Files from all users on this computer.
Windows will calculate what it can delete. This might take several minutes, please be patient.
After the results are ready, Disk Cleanup presents a list of solutions.
You can safely check all items in the Files to delete list except for Office Setup Files (in case you have Microsoft Office installed) without losing anything important. You can see more details about an item Description field after selecting it in the list.
If you experience frequent computer crashes (aka Blue Screens of Death, BSOD) and restarts, do not select Memory Dumps - use free WhoCrashed for analyzing crash dumps and determining causes of problems. After the problems have been resolved, it is safe to remove old memory dump files.
In Windows Vista, 7, 8, 8.1, and 10, you should not tick the Thumbnails option. Thumbnails are small previews of photos and videos available on your computer. You see those preview pictures while you browse your Pictures and Video folders or libraries. Unless you have recently deleted hundreds of video and photo files, you should leave Thumbnails deselected, because Windows will re-generate these anyway the next time you browse libraries with photos and videos (and the process slows down folder browsing for a while).
Windows 10 added the Delivery Optimization Files option to Disk Cleanup: this one uses space only when you've allowed Windows Update downloads from other PCs.
Disk Cleanup in Windows 10 October 2018 Update also has the option to clean up the Downloads folder. Use this one with extreme care, people often have at least something important left there.
This choice was removed again with Windows 10 May 2020 Update, and it will probably not return.
Windows XP offers to Compress old files - the files that have not been accessed or modified within the last 50 days. You can safely use this option, but please be aware that the process might take several hours to complete.
Click OK to start erasing unnecessary files.
Disk Cleanup will ask for your confirmation. Click Yes or Delete Files.
The cleanup might take quite a while, depending on how much data is selected for deletion.
The Disk Cleanup window will automatically disappear after the cleanup finishes. This leaves the Disk Properties window open.
If in Windows 7 and newer your device still has insufficient free space on its system drive, click the Disk Cleanup button again and let it clean up system files this time.
In Windows XP and Vista, try cleaning up System Restore points next.
Because Windows 7, 8/8.1, and 10 do not delete temporary System Files by default, you need to click the Clean up system files button. This also requires administrative rights.
Again, Disk Cleanup will scan for the files that can be removed. This might take a few minutes or so.
Basically, you will have the same options as described previously and you can safely choose everything except Office Setup Files. Those users who have installed a Windows XP/Vista/7 Service Pack will see an additional checkbox - Service Pack Backup Files. This one is safe to check in case Windows runs fine for at least a week after installing the Service Pack.
Windows 7 Service Pack 1, Windows 8/8.1, and 10 offer to remove outdated Windows Update packages and compress the remaining ones. Tick the Windows Update Clean-up checkbox for this to happen.
This option can greatly reduce the size of the WinSxS folder that has been known to eat up huge amounts of disk space since Windows Vista. One should never try deleting this important system folder or its files, just run Windows Update Cleanup instead.
Windows 10, 8.1, and 8 users can also invoke the same WinSxS cleanup by opening elevated Command Prompt or Windows PowerShell window and running the dism /online /Cleanup-Image /StartComponentCleanup command.
Cleaning up outdated Windows Update packages takes a long time: several hours in worst cases. You will also see the "Windows is configuring updates" message for at least 20-30 minutes upon the next shutdown or restart of your device.
The good side to this: many gigabytes of available disk space after the process completes.
If Windows 7 Service Pack 1 users who have applied the KB 2852386 update do not see the Windows Update Clean-up option, they need to download and run the System Update Readiness Tool and check the log for possibly missing updates. This process is thoroughly described in the Repair or reinstall Windows Update article.
Please note that using the Windows Update Clean-up option means that you cannot uninstall the outdated/removed updates, because they will be completely deleted from the WinSxS folder.
If Windows is running fine, you do not need to worry about this.
Windows 10 is also able to clean up old, unused Device driver packages. This can free several gigabytes of disk space and is selected by default.
Windows 10 October 2018 Update added the Downloads option here, but now it applies to all user accounts. Yes, ticking this checkbox removes all files from the Downloads folder of all user accounts. The Downloads checkbox was removed with Windows 10 May 2020 Update (version 2004).
As I warned before, Disk Cleanup with Windows Update Clean-up selected will take quite some time to complete (up to several hours in worst cases), and you'll see the "Windows is configuring updates" message for at least 20-30 minutes upon next shutdown or restart of your PC. Do not cancel either of these processes, or you might mess up Windows Update real bad!
Click OK to remove the unneeded files.
Disk Cleanup will ask for your confirmation. Choose Delete Files.
As in the previous example, the removal process might take several minutes and the dialog will close automatically.
Disk Cleanup window will disappear automatically after the process is complete.
There are numerous cases on Windows 10 devices (but also on Windows 7 and 8/8.1 computers) where the C:\Windows\Temp\ folder is filled with a large number of files by the name of cab_<number> files, for example, cab_923, cab_1024, etc. Some of the files are zero in size, while others are over 100 megabytes in size. This problem is most notable on devices with smaller drives, and the issue is usually caused by a bad logfile in the C:\Windows\Logs\CBS\ folder.
Just deleting the cab_xxxx files is only a temporary workaround, because Windows tries to recompress the bad log file every 30 minutes and recreates the files each time. That's why this issue has its own section here.
To resolve the issue, open Windows Explorer or File Explorer (keyboard shortcut Windows Key+E), navigate to C:\Windows\Logs\CBS\ folder (User Account Control might pop up, please accept the permissions change) and delete all files in the folder. This removes the bad log file that causes this behavior.
The log files are locked and cannot be removed while Windows Update is checking for or installing updates - the quickest solution to this is to restart your computer and then delete the log files as soon as possible.
Then navigate to the C:\Windows\Temp\ folder (again, User Account Control might pop up, please accept the permissions change) and delete all cab_<number> files. This probably frees massive amounts of disk space and keeps the files from being re-generated.
System Restore creates snapshots of Windows system and configuration files that you can later use to recover your computer to an earlier, working state. Every restore point uses quite a chunk of disk space, and if your device is working properly now, you can reclaim loads of disk space by deleting all restore points except the latest one.
Please note that you can set the maximum size of disk space used for System Restore in Windows XP, 7, 8/8.1, and 10 (see the first link in this paragraph). Windows Vista always uses up to 15% of disk space for System Restore, unless you manually reconfigure the Volume Shadow Copy service.
Shadow copies are used for creating System Image backups and Previous Versions of files in Windows Vista and 7. These copies ensure that even files that are in use and locked get backed up to create a complete and recoverable system image.
In Windows 8, 8.1, and 10, Previous Versions has been replaced by File History that uses less space on the system drive by keeping most backups on the selected external drive.
First, make sure your computer is working properly and you have no need for using System Restore. Restart your computer and verify everything is working fine.
If the Disk Cleanup window is not yet open, open Disk Properties, click Disk Cleanup and wait while the program calculates the space that can be freed by deleting temporary files.
In Windows Vista, make sure you use the Files from all users on this computer option in the prompt.
In Windows 7, 8/8.1, and 10, click the Clean up system files button first. Windows XP and Vista users should move on to the next step.
Now open the More Options tab. In the System Restore (in Windows XP) or System Restore and Shadow Copies section, click the Clean up button.
Disk Cleanup asks for your confirmation, choose Yes or Delete here:
Again, the Disk Cleanup window disappears after completing the job. Close the Disk Properties window after this.
All NTFS-formatted partitions/volumes support file and folder compression. This works best with common document formats, such as Word and Excel files, text files, and logs - the file size can decrease up to two times, sometimes even more. Picture, audio, and video formats that are already compressed (such as JPG, MP3, MP4, AVI) and most executable files do not compress that well.
NTFS compression has nearly no effect on performance while free disk space might increase noticeably.
Please note that this feature has nothing to do with Compressed (Zip) Folders in Windows. NTFS compression leaves files and folders usable by Windows and programs after applying the Compressed attribute, while Zip folders archive these into a single file that can be used by archiving utilities only.
You can usually get the best results by compressing the folder that contains users' files - Documents and Settings in Windows XP, or Users in Windows Vista, 7, 8, 8.1, and 10.
You should never try to compress a whole system drive (drive C:\, the partition where Windows is installed), or Windows folder or its subfolders - this will make your computer unbootable!
First, close all open programs and documents. Open Windows/File Explorer using keyboard shortcut Windows Key+E and open the drive where users' files are. In Windows XP, locate and right-click the Documents and Settings folder. In Windows Vista and later, locate the Users folder, click/touch it once to select it and then right-click/touch and hold it.
Choose Properties from the menu.
The Folder Properties window opens. Click or tap the Advanced button.
In the Advanced Attributes window, enable the Compress contents to save disk space option. Then click OK twice to close this window and the Folder Properties window.
Windows will confirm attribute changes. Leave the Apply changes to this folder, subfolders and files option selected and click OK.
In Windows XP, file and folder compression starts.
In Windows Vista and newer, you need to provide administrator permission next. Click Continue.
Please stand by. As usual, several system files are locked while a user is logged on to Windows. Click Ignore All in the first Error Applying Attributes window.
The compression process might take from 5 minutes to an hour, depending on how many files and subfolders there are. After the progress dialog disappears, you'll notice that the Documents and Settings / Users folder is now blue (if the Show encrypted or compressed NTFS files in color setting is enabled in Folder options). This indicates that the item is compressed using NTFS compression.
To see how much disk space you gained, right-click the folder and select Properties again.
Check the difference between Size and Size on disk fields. In the example below, users had a few personal files only, but settings and temporary files were compressed from 766 to 576 megabytes (compression rate is almost 25%).
You can also compress Program Files and ProgramData folders, but please do not attempt to compress the Windows folder or the whole system drive! System files must be uncompressed while Windows starts.
By now you should have sufficient disk space on your hard drive.
If there still is not enough available disk space, use CCleaner to clean up leftovers from well-known programs. You can also use the free tool for locating and removing duplicate and large files.
After you gain several gigabytes of disk space after these steps, it is recommended to defragment your hard drive (this does not apply to SSD-s) to optimize performance.