Windows sometimes refuses to compress files or folders — and the short answer is that the feature usually fails because the file system, file attributes, permissions, policy, or another program prevents NTFS compression from being applied. If you’re seeing that files won’t compress, this article shows why and how to fix it.
You’ll learn the most common causes of the issue and step‑by‑step fixes for each one, so you can get compression working again or choose an alternate approach. The problem topic is File compression doesn’t work in Windows 10 and this guide covers practical solutions and commands.
Key Takeaway
If Windows won’t compress a file or folder, check whether the volume supports NTFS compression, confirm the file isn’t already compressed/encrypted or locked, ensure you have permission (or run the compress command as admin), and use compact.exe or Windows Explorer’s Advanced Attributes to apply compression; for system-wide issues, check the NtfsDisableCompression registry value and free disk space or temporarily disable interfering software.
Quick Fix Guide
Quick Fix Guide
| Reason for the Problem | Quick Solution |
|---|---|
| Volume is not NTFS (FAT32/exFAT or some network shares) | Move to or convert the volume to NTFS or compress on the server. |
| File is already compressed (JPEG, ZIP, MP4, etc.) | Accept small gains or use a different format / archive to attempt further compression. |
| File is locked or in use by an application | Close the application, use Resource Monitor to find handles, or boot to Safe Mode. |
| Insufficient permissions | Take ownership (takeown) and grant full control (icacls) or run as Administrator. |
| NTFS compression disabled by registry/policy | Check HKLM\SYSTEM\CurrentControlSet\Control\FileSystem\NtfsDisableCompression and set to 0. |
| File is encrypted (EFS) | Decrypt the file (Properties → Advanced) or use cipher /d then compress. |
| System files or special files cannot be compressed | Do not compress pagefile/hiberfile; use compact /compactOS:always for Windows binaries only if suitable. |
| Antivirus/third-party tools interfere | Temporarily disable real‑time protection or add an exclusion, then retry. |
Detailed Fixes for “tu mets ici le problème du 8 reasons why File compression doesn’t work in Windows 10 (and how to fix it)”
H3 headings below correspond to the reasons listed in the Quick Fix Guide.
Why this causes the problem
- NTFS compression is a feature of the NTFS file system. Volumes formatted as FAT32 or exFAT do not support NTFS file-level compression. Some network shares (SMB) will not honor client-side NTFS attributes unless the server supports it.
Step-by-step solution
- Check the file system: right-click the drive in File Explorer → Properties and see File system (e.g., NTFS, FAT32).
- If the drive is FAT32/exFAT, either:
- Move the file/folder to an NTFS volume, or
- Convert the drive to NTFS without data loss: open Command Prompt (Admin) and run:
- convert D: /fs:ntfs (replace D: with the drive letter).
- Reboot if prompted.
- Note: Converting is generally safe, but have backups before major disk operations.
- For network shares: compress on the server (server volume must be NTFS) or copy files locally, compress, then move back.
Tips
- If a USB stick must be compressed, reformatting as NTFS is required (data backup needed).
2) File is already compressed (media or compressed archives)
Why this causes the problem
- Files like JPEG, PNG, MP4, MP3, and existing ZIP/7z archives are already compressed and typically won’t shrink further. NTFS compression may even slightly increase disk usage.
Step-by-step solution
- Identify file types that are already compressed (by extension).
- For many small text files you’ll see decent gains; for media files, expected gains are small.
- Use an archive tool (right-click → Send to > Compressed (zipped) folder or use 7-Zip with maximum compression) if you need a different container for distribution.
- Test compression ratio with compact /c filename to see effect:
- Open Command Prompt and run: compact /c “C:\path\to\file.ext”
Tips
- If you need more shrinkage for images, recompress with a different codec or lower quality, not NTFS compression.
3) File is locked or in use by an application
Why this causes the problem
- If a file is open and locked by a process, Windows may prevent changing attributes including compression.
Step-by-step solution
- Attempt to close the application that uses the file.
- If you don’t know which process, use Resource Monitor:
- Open Task Manager → Performance tab → Open Resource Monitor → CPU tab → use Associated Handles search box to search file name.
- Alternatively, use Process Explorer (Sysinternals) to find and close handles.
- If closing fails, reboot into Safe Mode and then apply compression.
- To compress via command line after ensuring no lock:
- compact /c /s:”C:\Folder” /i /Q (compress folder recursively).
Tips
- Avoid compressing open database or mail store files — these should be handled with application‑specific procedures.
4) Insufficient permissions
Why this causes the problem
- You need write permission to change a file’s attributes. For system or other users’ files, you may lack necessary rights.
Step-by-step solution
- Take ownership (requires admin):
- Open Command Prompt (Admin) and run:
- takeown /f “C:\path\to\file_or_folder” /r /d y
- Open Command Prompt (Admin) and run:
- Grant full control to your account:
- icacls “C:\path\to\file_or_folder” /grant %USERNAME%:F /T
- After permissions are fixed, attempt compression using Explorer: right-click → Properties → Advanced… → check Compress contents to save disk space, or use compact command.
- If the drive is system-protected, consider running the commands from an elevated prompt or WinRE.
Notes
- Changing permissions can create security risks; only modify permissions for files you own and understand.
5) NTFS compression disabled by registry/policy
Why this causes the problem
- Administrators can disable NTFS compression globally via policy or registry. If compression is disabled, attempts to compress won’t work.
Step-by-step solution
- Check the registry value that controls NTFS compression:
- Open Command Prompt (Admin) and run:
- reg query “HKLM\SYSTEM\CurrentControlSet\Control\FileSystem” /v NtfsDisableCompression
- If the output shows 0x1, compression is disabled.
- Open Command Prompt (Admin) and run:
- To re-enable NTFS compression, set the value to 0:
- reg add “HKLM\SYSTEM\CurrentControlSet\Control\FileSystem” /v NtfsDisableCompression /t REG_DWORD /d 0 /f
- Reboot after changing this value.
- If in an enterprise environment, check with your IT admin or Group Policy. Local Group Policy shortcuts: gpedit.msc → search for compression-related settings or consult documentation.
Caution
- Modifying registry values requires admin rights and a backup. Only change this if you understand the implications.
6) File is encrypted (EFS) and incompatible with compression
Why this causes the problem
- Windows cannot both EFS-encrypt and NTFS-compress the same file simultaneously. Encryption takes precedence or prevents compression.
Step-by-step solution
- Check if encrypted: right-click file → Properties → Advanced… and see if Encrypt contents to secure data is checked.
- To enable compression, decrypt first:
- Uncheck Encrypt contents to secure data and click OK, or run:
- cipher /d “C:\path\to\file_or_folder” in Command Prompt (Admin).
- Uncheck Encrypt contents to secure data and click OK, or run:
- After decryption, apply compression via Explorer or compact:
- compact /c “C:\path\to\file_or_folder”
Notes
- EFS encryption serves security purposes. Decrypting may expose data — only decrypt if you control security requirements.
7) System files or special files cannot be compressed
Why this causes the problem
- Windows does not allow certain system-critical files to be compressed (e.g., pagefile.sys, hiberfil.sys, some boot files). Attempting to compress them will fail or be ignored.
Step-by-step solution
- Compress user files but avoid compressing pagefile/hiberfil.
- If you need to reduce footprint of OS binaries, use Compact OS:
- Open Command Prompt (Admin) and run:
- compact /compactOS:always
- To revert: compact /compactOS:never
- Open Command Prompt (Admin) and run:
- If the system refuses compression for a file, move non-system data to another location and compress there.
Notes
- Compact OS is designed for systems with limited storage; test behavior and performance before broad deployment.
8) Antivirus or third‑party software interference
Why this causes the problem
- Real‑time protection or file filtering drivers can block modifications to file attributes or the compression process, causing it to fail.
Step-by-step solution
- Temporarily disable real-time protection in Windows Defender:
- Settings > Update & Security > Windows Security > Virus & threat protection > Manage settings → toggle Real‑time protection off.
- If you use third-party antivirus, pause real-time scanning or add the target folder to exclusions.
- Try compressing while protection is paused. When done, re-enable protection.
- If compression works with protection disabled, configure exclusions or consult the AV vendor for a safer exclusion.
Notes
- Don’t leave real‑time protection disabled longer than necessary. Use exclusions for trusted folders only.
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When to use NTFS compression vs compressed archives (ZIP, 7‑Zip) and alternatives
- NTFS compression is transparent: compressed files are used normally by applications and are decompressed on the fly. It’s good for many small files and for saving space on secondary drives.
- ZIP/7z archives are better for transferring or storing groups of files and often produce better compression ratios (especially with text) because they use stronger algorithms and can be re-compressed with different settings.
- How to create a ZIP quickly: select files → right-click → Send to > Compressed (zipped) folder. For better compression, install 7-Zip and use 7z with ultra compression.
- Use compact for on-disk, live compressing: compact /c /s:”C:\Folder” /i /Q — good for folders you access regularly without manual zipping.
- Consider third-party transparent compression tools (less common) only after research.
FAQ
Q: Can I compress the whole system drive (C:) with NTFS compression?
A: You can compress many user files, but compressing the entire system drive is not recommended. Use compact /compactOS:always for Windows binaries (supported scenario), but avoid compressing pagefile/hiberfil or critical boot components.
Q: How do I tell whether a file is compressed by NTFS?
A: In File Explorer, add the Attributes column or hover over the file; compressed files also show a blue filename (by default) and the compact command shows compression status: compact “C:\path\to\file”.
Q: How do I undo NTFS compression for a folder and files?
A: Use Explorer: right-click → Properties → Advanced… → uncheck Compress contents to save disk space, or use compact /u /s:”C:\Folder” /i /Q to uncompress recursively.
Q: Will compression slow down my PC?
A: It depends. Compression reduces IO but increases CPU usage; on fast CPUs with slow storage (HDD), performance can improve; on low‑power CPUs, decompression can add overhead. Test your workload.
Q: How do I check if NTFS compression is disabled system-wide?
A: Run: reg query “HKLM\SYSTEM\CurrentControlSet\Control\FileSystem” /v NtfsDisableCompression — a value of 0x1 means disabled; 0x0 means enabled.
Conclusion
When Windows refuses to compress files, the cause is almost always one of a small set of issues — file system type, file state (already compressed or encrypted), permissions, system policy, or third‑party interference. Use the steps above to diagnose and fix these conditions and, when appropriate, use compact.exe or ZIP/7‑Zip as alternatives. If you’re troubleshooting this problem, remember the core issue: File compression doesn’t work in Windows 10 — check file system, permissions, and policy first.
