How to Use NTFS Compression in Windows 11 and 10 to Free Drive Space Safely

What XDA Developers reported​

João Carrasqueira of XDA Developers turned on NTFS compression for his whole laptop drive. He reports:

• Data on the drive: 333 GB in use before compression.
• Time estimate: Windows predicted more than nine hours.
• Actual time: about two hours.
• Result: 68 GB of free space recovered (the headline says "over 60GB").
• Performance: he says he saw no noticeable slowdown on his modern laptop.

These numbers come from one person's laptop and one set of files. They are not a benchmark, and Microsoft does not promise any particular saving. Your result could be much bigger or much smaller depending on what you store. Still, roughly 20% of the used space came back from a single checkbox.

His reasons are easy to understand. He points to high storage and RAM prices in 2026, which push buyers toward cheaper laptops with less storage.

Section summary: One real-world test recovered 68 GB from 333 GB of data in about two hours. It shows what's possible, but it doesn't predict what you'll get.

How NTFS compression actually works​

This is not the same as making a ZIP file. With a ZIP, you pack and unpack files yourself. NTFS compression happens inside the file system, so you never see it.

According to Microsoft's Win32 developer documentation:

• It's invisible to apps. Programs only ever see the normal, uncompressed data, so existing software works without changes.
• It's lossless. Microsoft notes that it uses Lempel-Ziv compression, and unlike JPEG, no data is lost.
• It shrinks repeated data. It works by reducing redundancy, so how much you save depends on how repetitive your files are.
• It has limits. Microsoft says a file larger than 30 GB may not compress successfully.

That 30 GB point is easy to miss. It applies to each file, not to the whole drive. If you keep huge single files such as virtual machine disk images, some of them may not compress.

Folders follow a simple rule. Microsoft's documentation explains that a folder's compression setting is the default for new files and subfolders created inside it, and new items inherit that setting. That's why, as XDA notes, files you save later on a compressed drive or folder get compressed automatically.

The feature only works on NTFS. How-To Geek notes that this compression method only works on the drives formatted in the NTFS file system. It doesn't work for the drives that use the FAT32 or exFAT file system. If the checkbox is missing on a USB stick or SD card, that's usually the reason.

Section summary: Compression happens per file, without apps noticing, and without losing data. Folders pass the setting on to new files, and single files over 30 GB may not compress.

How to compress an entire drive in Windows 11​

Microsoft's own support page lists this method as a way to free space for installing important updates. The page applies to both Windows 11 and Windows 10.

1. Open File Explorer from the taskbar and select This PC in the left pane.
2. Right-click (or press and hold) the drive, usually C:, and choose Properties.
3. On the General tab, tick Compress this drive to save disk space.
4. Select Apply.
5. Windows asks what to apply the change to. According to NinjaOne's guide, you choose Apply changes to Drive [drive letter], subfolders, and files to enable compression. If you only apply it to the root, files already on the drive stay as they are.
6. Click OK and let it run.

Microsoft says that compressing the OS drive "does not delete the contents". That quote is from NinjaOne's summary; Microsoft's support page says the same thing in its own words and adds that you shouldn't have trouble opening or saving files afterward.

Expect it to take a while on a full drive. Windows' estimate can be far off, as XDA's nine-hour estimate versus roughly two real hours shows. FolderSizes notes that the time depends on the amount of data, the drive's speed, and your CPU - from minutes for a small data partition to several hours for a large, full drive. Plug a laptop into power before you start.

Some files will be skipped. XDA notes that files the system needs may not compress, and Windows may report access errors for files that are in use. Microsoft's command-line method (covered below) has an "ignore errors" switch for exactly this reason.

How to compress just one folder​

You don't have to compress the whole drive. To do one folder:

1. Right-click the folder and choose Properties.
2. On the General tab, click Advanced in the Attributes section.
3. Tick Compress contents to save disk space and click OK.
4. Click Apply. How-To Geek notes you can then pick Apply changes to this folder only or Apply changes to this folder, subfolders and files.

To check it worked, Tech2Geek notes that compressed files and folders will display their names in blue text in File Explorer, confirming that NTFS compression is active. You can also open the folder's Properties and compare Size with Size on disk.

XDA also suggests a no-wait option: create an empty folder, turn on compression, and save new files there. Because new items inherit the setting, it takes effect instantly and the savings build up over time.

Section summary: Use the drive checkbox to compress everything, or the Advanced button to compress one folder. Blue file names in File Explorer show it's on.

The command-line way for power users​

Microsoft's built-in compact command does the same thing from a command prompt. Microsoft's documentation lists it for Windows 11, Windows 10 and Windows Server 2016 through 2025. Useful options:

• compact on its own shows the compression state of the current folder and its files.
• compact /c /s compresses the current folder, its subfolders and the files already in them.
• compact /c /i /s:\, run from the root of a drive, compresses the whole volume. The /i switch keeps going when it hits errors instead of stopping.
• compact /u removes compression. Used on a folder alone, it only changes the setting for new files and leaves existing files as they are.

Microsoft also says compact can't compress FAT or FAT32 partitions. The same command has /EXE and /CompactOs options, but those are a different compression system meant for program and operating system files. Don't mix them up with the checkbox described here.

The trade-offs​

XDA admits there is a cost. Files have to be decompressed when they're read and compressed when they're written, and your CPU does that work. Carrasqueira thinks most modern PCs won't notice, but suggests that owners of older or slower machines think it over first.

Others are more cautious, especially about the system drive. FolderSizes, a company that sells disk-analysis software, says for rarely accessed data the overhead is irrelevant; for hot files it can noticeably degrade performance. It suggests clearing out junk before compressing C:.

Both views are reasonable, and the facts behind them don't conflict:

• Fast CPU, lots of documents and code: compression probably costs little and saves a lot.
• Older low-power laptop, files opened constantly: you may feel the slowdown.
• Photos, videos, music and game files: these formats are usually compressed already, so expect smaller gains. That's general industry knowledge, not a measured figure.
• Huge single files: Microsoft's 30 GB per-file limit applies.

Be skeptical of scary claims online. One partition-software vendor's page warns of crashes and data loss from NTFS compression while promoting its own product. Microsoft's documentation says the compression is lossless and that your files remain usable.

It's easy to undo​

You can reverse it. Microsoft says you can decompress the OS drive at any time by clearing the Compress this drive to save disk space checkbox and selecting Apply and then OK. Decompressing needs enough free space for the expanded files, so don't fill the drive with the space you just gained if you think you might switch it off later.

Other ways to free space​

NTFS compression keeps your files and stores them smaller. Windows has other tools that work differently:

A sensible order: empty the Recycle Bin and clear temporary files first, remove apps you don't use, and then compress what's left. Folders like Downloads and Documents are a good place to start.

What to try​

Here's a cautious plan for your own PC:

1. Check that the drive uses NTFS (look on the drive's Properties page).
2. Try one large folder full of documents first and compare Size with Size on disk.
3. If the savings look good and the PC still feels fast, compress the whole drive, with the laptop plugged in.
4. Use your PC normally for a few days. If anything feels slow, clear the checkbox to undo it.

XDA's 68 GB result won't be everyone's, but trying it costs nothing and you can undo it. If you try NTFS compression, tell us in the forum how much space you got back, what CPU you have, and whether you noticed any slowdown.