Quick fix: The hibernation file (C:\hiberfil.sys) is sized to your installed RAM — 16 GB RAM = 16 GB hibernation file. If you don’t use hibernate: open Terminal (Admin) and run powercfg /h off. The file is deleted immediately. To shrink without removing: powercfg /h /size 50 caps at 50% of RAM.

Storage running low. WizTree shows C:\hiberfil.sys eating 16 GB or more. The file is for Hibernate mode (full RAM state saved to disk on shutdown, restored on next boot). On PCs with large RAM (32, 64 GB), the file is correspondingly huge. If you don’t use Hibernate, removing the file recovers significant space.

Symptom: hiberfil.sys consuming 10–64+ GB of C: drive space.
Affects: Windows 11 (and Windows 10).
Fix time: ~3 minutes.

What causes this

The hibernation file is sized to fit the contents of RAM during a hibernate event. With 32 GB RAM, the file is around 24–32 GB. Modern Windows 11 also uses hiberfil.sys for Fast Startup — when you shut down with Fast Startup enabled, kernel state is saved to hiberfil.sys to restore on next boot. Even if you never use Hibernate from the menu, Fast Startup uses it.

If you use Sleep instead of Hibernate, and want to skip Fast Startup’s slight boot speed gain, disabling hibernate entirely recovers all the space.

Method 1: Disable hibernation entirely

The fastest recovery.

Open Terminal (Admin): right-click Start → Terminal (Admin).
Run:
```
powercfg /h off
```
The hibernation file is deleted immediately. C: free space increases by the file size.
Side effect: Fast Startup also disables (relies on hiberfil.sys). Boot may be 5–10 seconds slower. Sleep is unaffected.
To verify deletion: open File Explorer with Show hidden files and Show protected operating system files enabled (via Folder Options → View). C:\hiberfil.sys should no longer exist.
To re-enable: powercfg /h on. File recreates with default size.

This is the right path for users who use Sleep instead of Hibernate.

Method 2: Shrink hibernation file without disabling

For users who want Hibernate but smaller file.

Open Terminal (Admin).
Set hibernation file to a percentage of RAM:
```
powercfg /h /size 50
```
50% of RAM. Minimum is 50%; can’t go lower without disabling.
To check current size: powercfg /a lists available sleep states; fsutil file queryextents C:\hiberfil.sys shows file extents.
For Hibernate to still work with reduced file: Windows compresses kernel state to fit. Compression saves typically 30–50%, so 50% file size is workable for most setups.
Trade-off: with reduced hibernation file, very full RAM (16+ GB used) may fail to hibernate. Save your work before triggering hibernate.
Reset to default: powercfg /h /size 75. Restores larger file.

This is the right approach when you actively use Hibernate.

Method 3: Use Fast Startup without full Hibernate

For users who want Fast Startup but not full Hibernate menu option.

Disable Hibernate option but keep Fast Startup: powercfg /h /type reduced. Hibernate is unavailable in the power menu; Fast Startup still works (uses smaller hiberfil.sys).
Reduced hibernation file is about half the size of standard.
To check: powercfg /a. Should show Hibernate as unavailable but Fast Startup’s hiberfil.sys still present.
For PCs that need both Fast Startup AND Hibernate: powercfg /h /type full. Original behavior.
For tablet-like 2-in-1 with Modern Standby: hiberfil.sys may not be needed at all. Check powercfg /a for Modern Standby vs. S3 sleep status. Modern Standby PCs typically don’t use hibernate.

This is the right approach for balanced setups.

How to verify the fix worked

Check C: free space before and after. Should match the hiberfil.sys size you saw in WizTree.
Run powercfg /a in Terminal. Output shows current sleep states. Hibernate listed as “not available” after Method 1.
Verify file removed: WizTree shows no hiberfil.sys, or much smaller.

If none of these work

If hiberfil.sys doesn’t shrink or disappear after powercfg command: Need admin elevation: ensure Terminal is running as Administrator. Right-click Terminal in Start menu → Run as administrator. Group Policy preventing change: corporate PCs may have policies. Check via gpresult /h C:\result.html — look for Power Management policies. For PCs where hiberfil.sys reappears after disabling: Windows feature updates can re-enable hibernate. Re-run powercfg /h off after major updates. For really large hiberfil.sys: ensure /size hasn’t been set artificially high. fsutil file queryextents C:\hiberfil.sys shows actual size. For BitLocker-encrypted drives: hibernate file is encrypted; the size is the same regardless. For NVRAM-cached hibernate: some modern firmware caches small hibernate state in flash. Doesn’t affect hiberfil.sys on SSD.

Bottom line: powercfg /h off disables hibernate and deletes hiberfil.sys, freeing space equal to RAM size. powercfg /h /size 50 reduces file by ~50% while keeping Hibernate functional.