WinDirStat is a free, open-source directory size reporting tool that derives its name from a portmanteau of the words Windows Directory Statistics. WinDirStat is published under version 2 of the GNU General Public License.

FolderSizes is a commercial disk space analysis and reporting tool from Key Metric Software. FolderSizes offers a free trial period and affordable licensing options, including a discounted personal edition for home use.

The developers of FolderSizes publish this article in hopes of encouraging readers to download and try both disk space analysis tools before deciding which is best for your needs. We'll be comparing performance, features, accuracy, security, and version history for both tools.


Objective testing reveals FolderSizes to be much faster than WinDirStat in terms of disk space analysis performance and user interface responsiveness.

In a test environment utilizing a local solid-state drive containing 1,551,271 files and 308,966 folders, WinDirStat finished its file system analysis in just under 3 1/2 minutes. FolderSizes completes its analysis of the same target in 26 seconds.

Next, we analyzed a mechanical hard drive containing 1,654,846 files and 22,976 folders. The results were pretty similar, with WinDirStat performing the analysis in just over 3 1/2 minutes and FolderSizes finishing in just under 15 seconds.

The performance disparity was even more significant when analyzing remote (network) file systems. Analyzing a network share containing 278,024 files and 64,271 folders took WinDirStat just over 9 minutes. FolderSizes completed the same analysis in 33 seconds.

The WinDirStat user interface became unresponsive frequently during our tests, especially when displaying analysis results.


As a commercial product, FolderSizes has many more features than WinDirStat. This is likely unsurprising since FolderSizes has been undergoing continuous development since 2003. For this reason, we'll only touch on this topic briefly.

Features exclusive to FolderSizes include:

  • Scan filtering
  • Export reports to HTML, Excel, PDF, and more
  • File system snapshots
  • Trend analysis
  • Built-in scheduling
  • Email integration for report delivery
  • Built-in file and folder metadata search
  • An advanced command-line interface
  • Largest, oldest, and newest file reports
  • Temporary and duplicate file reports
  • File type, attribute, and owner reports
  • File owner, size, name, age, and depth reports
  • Various themes, including dark mode
  • And more


FolderSizes is considerably more accurate than other file system analysis tools due to its deep understanding of NTFS file system structures.

And by accuracy, we're specifically referring to the software product's ability to produce results that reflect the actual file system state.

The screenshots below offer a real-world example of how the accuracy of these tools differs. FolderSizes shows the Windows folder of this operating system drive as containing 330,988 files for a total folder size of 38.3 GB.

FolderSizes report

If we compare this to the size metrics reported by Windows, we will see that they match.

Windows report

However, WinDirStat reports that this same Windows folder contains 324,762 for a total size of 35.3 GB. In this instance, WinDirStat is not "seeing" thousands of files present in this folder - even though they clearly exist, as reported by both Windows and FolderSizes.

WinDirStat report

Although WinDirStat consistently produced correct results for simple file system structures, we found many other examples of inaccuracies.


FolderSizes is developed and published by Key Metric Software, operating entirely within Michigan, USA, since its inception in 2003. The FolderSizes product installer carries an extended validation certificate, making it easy to verify its origin.

Each FolderSizes release undergoes extensive testing for conformance to best software development security practices and is always verifiably free of malware. Our developers engage in continuous monitoring of emerging security vulnerabilities.

Key Metric Software supports over 60,000 customers and hundreds of thousands of product installations worldwide.


According to Wikipedia, the last stable release of WinDirStat became available in 2007 - approximately 14 years ago at the time of this writing.

FolderSizes has undergone hundreds of product release cycles since its initial release in 2003 and supports all modern Windows operating systems.

Start reaping the benefits of this powerful tool today!

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