NTFS COMPRESSION

How to Compress a Drive to Save Disk Space in Windows

NTFS compression is a free, built-in Windows feature that compresses files on disk and decompresses them automatically whenever they are used - no zip utilities, no manual steps. Applied to the right files, it can recover 30–60% of the space those files occupy. This guide explains when NTFS compression makes sense, how to apply it to a drive, folder, or individual file, and how to measure the results.

Why NTFS Compression?

Unlike archiving files with a compression utility, NTFS compression is completely transparent: compressed files open, edit, and save exactly like normal files, with Windows handling the compression behind the scenes. You can apply it at any level - a single large file, a folder (including everything inside it), or an entire drive.

The only hard requirement is that the volume must be formatted with NTFS; FAT32 and exFAT drives do not support it. To check, right-click the drive in File Explorer, choose Properties, and look at the File system field on the General tab.

Which Files Compress Well (and Which Don't)

Compression savings vary enormously by file type. Good candidates (often 30–60% smaller):

• Office documents - older .doc/.xls formats, plus databases (.mdb, .accdb)
• Text-based files - logs, .txt, .xml, .json, .csv
• Uncompressed images - .bmp, .tiff
• Email archives - .pst, .ost

Poor candidates (usually under 5% savings, but still costing CPU on every access):

• Compressed media - .jpg, .png, .gif images; .mp4, .mov, .avi video; .mp3, .aac audio
• Archives and installers - .zip, .rar, .7z, .exe, .msi

Not sure what a drive contains? The FolderSizes File Types report breaks down storage by extension, showing exactly how much space each file type consumes - a fast way to judge whether a volume is a good compression candidate before you commit.

Performance Considerations

Windows decompresses a file every time it is read and recompresses it when written, which costs CPU time. For rarely accessed data the overhead is irrelevant; for hot files it can noticeably degrade performance. NTFS compression works best on infrequently accessed document folders, reference archives, and old project data you must retain but seldom open. Avoid compressing system files, program folders, and anything you use many times a day.

Think twice before compressing your OS drive (usually C:). Windows skips files it cannot safely compress, but operating system files are read constantly, so the CPU overhead is felt everywhere. Compression pays off most on data drives and archive folders - and freeing space on the system disk is usually better achieved with disk cleanup techniques like removing temporary files, large unused files, and duplicates first.

How to Compress a Drive in Windows

Administrator rights are required to compress a whole drive:

1. Open File Explorer and locate the drive you want to compress.
2. Right-click the drive and select Properties.
3. On the General tab, check "Compress this drive to save disk space."
4. Click Apply, then OK.
5. In the Confirm Attribute Changes dialog, choose whether to apply compression to subfolders and files, then confirm.

The larger and fuller the drive, the longer compression takes - anywhere from minutes to several hours. You can keep using the computer while it runs.

How to Compress a File or Folder in Windows

To compress a folder (or a single file) in place - without turning it into a zip archive:

1. In File Explorer, navigate to the file or folder.
2. Right-click it and select Properties.
3. On the General tab, click Advanced.
4. Check "Compress contents to save disk space" and click OK twice.
5. For folders, choose whether the change applies to subfolders and files when prompted.

NTFS Compression vs. Zipping Files

When people search for how to compress files on Windows, they often mean zip files - the "compressed (zipped) folder" option in File Explorer. Zipping and NTFS compression solve different problems. A zip archive is a new, separate file: ideal for emailing or sharing a reduced file size, consolidating thousands of small files into one, and moving data to drives or cloud storage where NTFS compression doesn't travel. NTFS compression, by contrast, is invisible - files stay exactly where they are and remain directly usable, with Windows compressing them behind the scenes.

A practical rule of thumb: zip what you're archiving or sending; NTFS-compress what you're keeping but rarely touching. FolderSizes supports both workflows - it can zip files directly from any report or search result (with optional AES-256 encryption) and measure the savings from NTFS compression across entire drives.

Measuring the Savings with FolderSizes

File Explorer can only show compression results one item at a time. FolderSizes reports both size (logical bytes) and size on disk (allocated bytes) for every file and folder it scans, so a single pass shows exactly how much space NTFS compression is saving across an entire drive or folder tree. The File Attributes report also lists every compressed file on a volume, making it easy to audit what is - and isn't - compressed.

Compression is just one tool in the disk-cleanup toolbox. Before compressing, it is usually worth finding content you can remove outright: use the Largest Files and Duplicate Files reports to spot deletion candidates, and see our 13 ways to recover disk space for a complete cleanup strategy. The Trend Analyzer can then track disk usage over time so space problems don't sneak back.