What the software actually measures
Windows File Explorer tells you how large a single file is. It does not tell you which of the 40,000 folders on your system drive grew by 60 GB last spring. TreeSize answers that second question: it walks the directory tree, adds up the files inside every branch, and presents the result as a sortable tree where the largest folder is always at the top.
The practical effect is that a disk cleanup stops being guesswork. Instead of opening folders one by one, you follow a single descending chain — drive, then the heaviest top-level folder, then the heaviest folder inside it — until you reach the files that are responsible for the missing space.
The three numbers people confuse
- Size is the logical size of the data, the number you see in a file's properties dialog.
- Allocated space is what the file system actually reserves on disk. On a volume with a 4 KB cluster size, a 300-byte shortcut still occupies 4 KB, so a folder full of tiny files can be much heavier in allocated terms.
- Percent of parent is how much of the folder above a branch consumes. This is the column that makes a cleanup decision obvious, because it tells you whether a folder is worth opening at all.
Switching the display between these values changes which folders look important. When a scan result surprises you, check which of the three is currently shown before you conclude that something is wrong. Our troubleshooting page covers the cases where the numbers genuinely do not add up.
Which edition fits which job
TreeSize is published in more than one edition. The free edition covers the classic home task — find the big folders, clear some room, move on. The paid editions add search, reporting, scheduling and duplicate detection, which is where administrators spend most of their time.
| Situation | Usually enough | Where you run out of room |
|---|---|---|
| Home PC running out of space on C: | TreeSize Free | Nothing — a folder tree plus a treemap answers the question |
| Recurring cleanup across several machines | A paid edition | Free has no scheduled scans and no saved report formats |
| File server and network share reporting | TreeSize Professional | Free is licensed for private use and is not built for server reporting |
| Hunting duplicate files across drives | TreeSize Professional | Duplicate search is not part of the free edition |
We keep a side-by-side breakdown on the TreeSize Free vs Professional page, including the licensing question that trips up people who install the free edition at work.
Typical use cases on Windows
Home users on Windows 11 and Windows 10
The usual culprits are game installations, video exports, cloud-sync folders that kept a local copy, and browser caches. A scan of the user profile normally explains most of a full system drive in under a minute. Step-by-step instructions live on our Windows 11 and Windows 10 pages.
IT staff and system administrators
Here the value is in repeatability: scan a share, export the result, compare it against last month, and hand the departments a list they can act on. Scans over SMB are slower than local scans, and the account you run them under decides how much of the tree you can actually read — see scanning a network drive.
Anyone auditing an external disk
Backup drives collect years of half-finished archives. Because the scan is read-only until you delete something yourself, an external drive is a safe place to start if you have never used a disk space analyzer before. We walk through it in scanning an external drive.
Reading a scan without breaking Windows
A disk space analyzer shows size, not importance. Several of the largest folders on a Windows system are supposed to be large, and removing them by hand causes problems that are far more expensive than the space you recover.
C:\Windows\WinSxSlooks enormous because of hard links; its real footprint is smaller than reported and it must be cleaned through Windows tooling, not manually.hiberfil.sysandpagefile.sysare managed by the operating system. Change them through system settings if at all.- Cloud folders for OneDrive, Dropbox or Google Drive may hold local copies of files you think live only in the cloud. Deleting them in File Explorer can delete the cloud copy too.
AppDataholds settings and licenses alongside caches. Clear caches from inside the application that owns them.
Our checklist for making these calls is on deleting large files safely.
How this site works
jam-software.org is an independent editorial site. We are not the developer of TreeSize and we do not host installers. When a question depends on something only the vendor can confirm — current version numbers, license terms, system requirements — we point you at the developer instead of inventing an answer.
Our sourcing and correction rules are written down in the editorial policy.
Common questions about TreeSize
Is TreeSize the same thing as WinDirStat?
No. They are separate programs from different developers that solve a similar problem. Both display where disk space went; they differ in interface, scan behavior and the feature sets of their paid or free versions. We compare the options on the alternatives page.
Does a scan change anything on my disk?
Why is the reported folder size different from File Explorer?
Can I use it on Windows Server?
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