What is taking up space on my C: drive?

Open Settings → System → Storage — it shows the real breakdown, including categories File Explorer hides. On most PCs the biggest items are Windows Update leftovers (often 10–20 GB), the hibernation file, and system restore points, not your own documents.

Is it safe to delete Windows.old?

Yes, once the update has gone in fine and you have been using the PC since. It is a copy of your previous Windows version kept so you can roll back, and Windows removes it automatically after 10 days. Delete it through Settings → System → Storage → Temporary files, not by hand — never delete anything out of C:\Windows yourself.

How do I free up space without deleting my files?

Clear Windows Update leftovers, turn hibernation off with powercfg /hibernate off if you never hibernate, cap restore points at about 5%, and set OneDrive files to online-only with Free up space. Between them that is usually 20–40 GB and none of it touches your own documents.

Should I use a PC cleaner app to fix a full C: drive?

You don't need one. Everything that safely frees real space is built into Windows — Settings → System → Storage, Disk Cleanup, Storage Sense and powercfg. Cleaner apps mostly repackage those, and the aggressive ones delete things that matter.

How much free space should Windows have?

Keep at least 10–15% of the drive free. Windows uses spare space as overflow memory and as working room for updates, so a drive close to full gets slower and updates start failing before it is completely out.

C: Drive Full on Windows? How to Find What's Using It (2026)

Windows warns you the C: drive is nearly full, you go looking, and your own files don't come close to accounting for it. On most PCs the space has gone to things Windows keeps out of sight on purpose — rollback copies of updates, snapshots, a hibernation file, and cloud folders that quietly downloaded themselves.

Almost all of it is safe to clear with built-in tools, and you don't need a cleaner app. Below are the causes, biggest first. Do it by hand, or let Noah find what's actually taking the space and clear it with your approval (more at the end).

Never delete files out of C:\Windows yourself. Everything below has a proper tool for it, and hand-deleting system files is how a full drive turns into a PC that won't boot.

First, see where the space actually went

Before deleting anything, look at the real breakdown. Windows has this built in and it counts the hidden categories that File Explorer leaves out — which is exactly why your own folders never add up to the missing space.

Fixopen Settings → System → Storage. Wait for it to finish measuring, then read the list top down. Whatever sits at the top is what to deal with first — and it is very often Temporary files or System & reserved, not Documents.

NoahNoah measures the drive the same way, but explains each category in plain terms: what it is, whether it is safe to clear, and how much you would actually get back. It clears the ones you approve.

Windows Update leftovers

A large Temporary files or Windows Update Cleanup entry, usually after a big Windows version update.

When Windows installs a feature update it keeps the previous version so you can roll back if the new one causes problems — in a folder called Windows.old. That copy is routinely 10–20 GB, and it is the single biggest recoverable chunk on most full drives. Windows deletes it by itself after 10 days; if you're out of space now, you don't have to wait.

Once removed, you can no longer roll back to the previous Windows version. If the update went in fine and you've been using the PC since, that isn't worth 20 GB.

Fixin Settings → System → Storage → Temporary files, tick Windows Update Cleanup and Previous Windows installation(s), then Remove files. It can take several minutes and looks stalled partway through — let it finish.

The hibernation file

Several gigabytes unaccounted for, on a desktop that never hibernates.

Hibernating writes everything in memory to a hidden file on C: called hiberfil.sys, so the PC can shut down fully and come back where it was. That file is reserved whether or not you ever hibernate, and it is sized against your memory — 16 GB of RAM means several gigabytes gone on a desktop that only ever sleeps.

One thing to know before turning it off: Windows' Fast Startup uses this same file, so switching hibernation off also disables Fast Startup and boots will be a little slower. On an SSD the difference is small.

Fixopen Command Prompt as Administrator (right-click Start → Terminal (Admin)) and run:

zsh — Terminal

% powercfg /hibernate off

Deletes hiberfil.sys and frees space matching your RAM. Reverse it any time with powercfg /hibernate on. Laptop users who hibernate should skip this one.

System restore points

A large System & reserved figure that grows steadily over months.

A restore point is a snapshot of system settings and files taken before updates and installs, so you can go back if something breaks. They're worth having — but Windows lets them expand to a set share of the drive, and on a smaller drive that share is a lot of space.

Fixpress Start, type Create a restore point, select the C: drive and click Configure. Drag Max Usage down to around 5%. Keep protection on — the point is to cap it, not remove your safety net. Use Delete there only if you're desperate for space right now and the PC is working correctly.

OneDrive downloaded everything

A OneDrive folder as large as your whole cloud storage, often after a reinstall or new sign-in.

OneDrive can keep files online-only — visible in File Explorer but not taking space until you open one. But Always keep on this device gets switched on easily, sometimes by default after a reinstall, and then your entire cloud drive is copied onto C:.

Fixin File Explorer, right-click the OneDrive folder and choose Free up space. The files stay listed and download on demand when you open them. To stop it recurring, right-click the OneDrive cloud icon → Settings → Sync and back up → Advanced settings and confirm Files On-Demand is on.

Downloads, temporary files and the recycle bin

A large Downloads folder or a Recycle Bin nobody has emptied.

Installers sit in Downloads for years, and deleting a large file only moves it to the Recycle Bin — where it still occupies the drive until the bin is emptied.

Fixsort Downloads by size and clear out the installers you've already used, then empty the Recycle Bin. Then turn on Storage Sense (Settings → System → Storage) so Windows keeps doing this for you — it clears temporary files and old Recycle Bin contents on a schedule.

If it's still full and nothing explains it

When the total still doesn't add up, it is almost always one application storing something large somewhere unexpected — game installs, virtual machine disks, video project caches, or a backup tool writing locally.

Fixcheck the folder sizes directly. In an Administrator Command Prompt:

zsh — Terminal

% dir C:\ /s /-c | sort /r /+1 | more

Slow but built in, and needs no download. It walks the drive and shows sizes so you can find the folder that stands out. Press Ctrl+C to stop it early.

Commands in this guide are standard, read-only macOS diagnostics unless noted; anything that changes your system is called out. When in doubt, back up first with Time Machine.

C: drive full? Here's what's actually using the space