The three free Windows disk analysers, and why one is far faster
WizTree reads the file table directly, which is the difference between a scan in seconds and one in minutes. All three compared honestly.
Windows has three well known free disk analysers and one of them works in a fundamentally different way, which is worth understanding before choosing.
The difference that matters
WinDirStat and TreeSize walk the folder tree, asking the file system about each folder in turn. WizTree reads the Master File Table directly on NTFS volumes, which is the index NTFS already maintains of every file on the drive. Reading one index is dramatically faster than walking a million folders, and WizTree's own page claims 46 times faster than WinDirStat.
That is not marketing so much as a different approach: it is the same reason Everything finds files instantly. The trade is that it needs administrator rights to read the MFT, and it only applies to NTFS.
The three, honestly
| WizTree | TreeSize Free | WinDirStat | |
|---|---|---|---|
| Cost | Free for personal use | Free, non commercial | Free, open source |
| Speed | Seconds, via the MFT | Minutes on a large drive | Slowest of the three |
| View | Treemap and list | List, with a treemap view | Treemap, classic |
| Needs admin | Yes, for MFT reads | No | No |
| Maintained | Yes | Yes | Barely, and it shows |
Which to use
- WizTree if you want an answer now and the drive is NTFS. It is the one to reach for first.
- TreeSize Free if you want a clean list without administrator rights, or you are on a network drive.
- WinDirStat if you specifically like its treemap and do not mind waiting. It is the oldest and the least maintained.
- SpaceSniffer is a fourth option, portable and visual, and worth knowing if you like its layout.
What none of them tell you
All four measure bytes per path, which is exactly what they promise. None tells you whether a 6 GB folder is a cache that rebuilds itself, an application's only copy of your data, or a leftover from software you removed in 2023. On Windows that distinction is sharper than on a Mac, because the Installer folder looks like a cache and is not, and WinSxS looks twice its real size to any tool that walks it.
Common questions
Which is the fastest disk analyser for Windows?
WizTree, because it reads the NTFS Master File Table directly rather than walking folders. Its own page claims 46 times faster than WinDirStat, and the approach is why.
Is TreeSize Free actually free?
Yes, listed at zero, for personal non commercial use on desktop systems. Its FAQ notes it is not usable on Windows Servers, which is what the paid editions are for.
Is WinDirStat still worth using?
It works and it is open source, but it is the slowest of the three and barely maintained. WizTree or TreeSize Free will answer the same question faster.
Why do disk tools report different sizes for WinSxS?
Because the component store is built from hard links and any tool that walks folders counts the same bytes once per name. DISM's AnalyzeComponentStore is the only correct measurement.