When the C drive is full, the cause is usually one of five things: personal files such as videos and downloads, installed apps and games, temporary and cached data, files that Windows keeps for itself, and cloud files that are stored locally. The Storage page in Settings shows a rough split. File Explorer, a short PowerShell command and the Properties dialog fill in the rest. None of these change anything, so you can look freely before you decide what to remove.
Start with the Storage page
Open Settings, then System, then Storage. Windows scans the system drive and shows a bar split into categories. Select a category to see what is inside it. Names and groupings vary between Windows 10, Windows 11 and individual builds, and a typical list includes apps, temporary files, documents, pictures and a system and reserved group. If your screen differs, follow the same idea with the labels you see.
Storage Sense covers only the system drive, according to Microsoft's Storage Sense page (checked in October 2026). For other drives, go to Advanced storage settings, then Storage used on other drives.
The numbers on this page are estimates. Treat the biggest category as a place to look next, not as a verdict.
Check installed apps by size
In Windows 11, go to Settings, Apps, Installed apps. In Windows 10, use Apps & features. Both lists can be sorted by size. Games, creative software and development tools are the usual suspects, and a single game can take tens of gigabytes. An app you have not opened in a year is a candidate for uninstalling, and you can reinstall it later.
Find the biggest folders and files
File Explorer's Details view shows the size of files but not folders. To see how big a folder is, right-click it, choose Properties and wait for the size to be calculated. The dialog shows both Size and Size on disk, and these can differ.
Microsoft's guide to freeing up drive space suggests opening the Videos, Music, Pictures and Downloads folders first, because they usually hold the largest files. Switch to Details view, right-click an empty area, and choose Sort by, then Size.
The File Explorer search box also accepts a size filter. Microsoft's Advanced Query Syntax reference shows that a number after size: is read in bytes, so size:>1000000000 finds items larger than about 1 GB. Open the folder you want to search first, because searching the whole drive can take a long time.
Ask PowerShell for the 20 largest files
This command only reads. It lists the 20 largest files under a folder you choose. Replace the path with your own user folder, and expect it to take a while on a large one.
Get-ChildItem "C:\Users\YourName" -Recurse -File -ErrorAction SilentlyContinue |
Sort-Object Length -Descending |
Select-Object -First 20 FullName, @{Name="GB"; Expression={[math]::Round($_.Length / 1GB, 2)}}
The command comes from the standard Get-ChildItem cmdlet. Keep it to one folder at a time. Running it on the whole drive can pass through system folders and links, and the totals become hard to read. We have not tested this exact line on every Windows 10 and 11 build, so read the output before you act on it.
Understand cloud placeholders
If you use OneDrive, a file can show in File Explorer without being on your disk. Microsoft's page on OneDrive Files On-Demand says a blue cloud icon marks an online-only file, and that online-only files do not take up space on your computer. Opening one downloads it and makes it a locally available file.
Two things follow. First, a folder that looks huge in a listing may take little space. Check Size on disk in Properties. Second, tools that read every file, including a scan or a script, can trigger downloads of online-only files, so avoid pointing them at your OneDrive folder unless you want that. To give space back, right-click a file or folder and choose Free up space.
Look for what Windows keeps for itself
Some of the largest items are hidden or protected. To see hidden items in File Explorer, open the View menu and turn on Hidden items. Then look at the root of C:.
hiberfil.sysstores the contents of memory when the PC hibernates. Microsoft says its size is approximately equal to the amount of RAM installed.pagefile.sysis the page file, which Windows uses when memory runs short. Microsoft's article says page files are system managed by default, and has a page file sizing article if you want the details.Windows.oldexists for a period after a Windows upgrade. Microsoft says it is deleted automatically ten days after you upgrade.- Restore points are stored by System Protection. Microsoft's System Protection page says you can configure how much disk space they use.
- The
WinSxSfolder is the component store. File Explorer overstates its size, as explained below.
These are covered one by one, with the supported way to reduce each, in our system files guide. For now, treat them as numbers to understand, not files to delete.
Why WinSxS looks bigger than it is
Microsoft explains that files in WinSxS can appear to be stored in several places in the operating system, but usually there is only one copy and the rest are hard links. Some tools, including File Explorer, add up directory sizes without accounting for hard links, which makes the folder look bigger than it really is. To see the actual figure, open Command Prompt as administrator and run Dism.exe /Online /Cleanup-Image /AnalyzeComponentStore, which reports both the Explorer-reported size and the actual size. The command only analyses. See Microsoft's page on determining the actual size of the WinSxS folder.
What you found, and what to do next
| What you found | What it usually means | Safe next step |
|---|---|---|
| Videos, photos or Downloads dominate | Personal files, many of them old | Move to an external drive or the cloud, check the copy, then remove |
| One or two games or tools take tens of GB | Large installed apps | Uninstall what you no longer play or use |
| Large OneDrive folder, little real use | Mostly online-only placeholders | Check Size on disk, then use Free up space where needed |
| hiberfil.sys is large | Hibernation is on | Decide whether you use hibernate or Fast Startup |
| WinSxS looks enormous | Hard links counted more than once | Run AnalyzeComponentStore before doing anything |
| Many large files with similar names | Possible duplicates | See the duplicates guide |
What not to do while investigating
- Do not delete anything inside
C:\Windows,Program FilesorProgramDatabecause it is big. Large does not mean unnecessary. - Do not take ownership of
System Volume Informationto look inside it. - Do not delete files by size alone. Sorting by size tells you where to look, and nothing about whether a file matters.
- Do not run a command you do not understand with administrator rights.
Find what fills your C drive with SafeClean
SafeClean shows used and free space for every drive as soon as it opens, with a breakdown by apps, videos, photos, documents, downloads and temp files. Its largest-files view lists the biggest files on each drive with a Show in Explorer button. Removing a file from that list is a separate step that moves it to the Recycle Bin after you confirm.
Get SafeClean on Microsoft Store Features and pricing
Frequently asked questions
Why does my C drive fill up when I save files to another drive?
Some apps and Windows features default to C:. In Windows 11, Settings, System, Storage, Advanced storage settings, Where new content is saved lets you change the default drive for some content types. Apps that store their own data elsewhere, such as browsers and games, need their own settings changed.
Why do File Explorer and the Storage page show different numbers?
They measure differently. File Explorer can count hard-linked files more than once, as Microsoft notes for WinSxS, and cloud placeholders list a size without using that space on disk. Neither number is wrong. Use Size on disk for the amount actually stored.
Can I shrink the System and reserved category?
Partly. It contains items such as the hibernation file, the page file and restore points, which have supported settings. It also holds files Windows needs. Use the supported controls in the system files guide and leave the rest alone.
Is a full C drive a sign of a virus?
Usually not. Microsoft's drive space guide does mention that malware can use significant space and suggests a scan with Windows Security if you suspect infection. A drive filled by videos, apps and caches is far more common.