Wrong calculation of folder size by Windows

I think it is unbelievable that an operating system is not able to show an accurate count of files and sizes.

This is... some kind of "basics" of OS since they exist. Incredible.

Today I was updating my backups and I was wondering where 50 GB were gone. WinMerge application told me both versions were exactly the same, but Windows tells me there are 50 GB of difference. Non-sense.

And even in both versions, the count is not correct, so the difference is even bigger.

@Allan747, MN79 and other users discussing this problem

I had posted earlier in this thread and since then had explored this problem further in my computer. I have always installed the most recent Windows 10 updates and can confirm that as of the present, the problem still persists and has not been solved by Microsoft. Some users including MN79 suggested downloading certain (non-Microsoft) programs that enable showing the tree of sub-folders with their correct sizes and then renaming those files with filenames that have too many characters. I did not try that out, but their suggestions led me to suspect that the excessive lengths of filenames (including file paths) could at least be one important source of the problem.

Based on my experimentation, it appears that Windows 10 cannot detect folder sizes correctly when the folder contains subfolders (and further and further subdivisions into subfolders) so that finally the filenames (inclusive of file paths) exceed a certain number of characters. To illustrate, Windows might show the size of folder A correctly if A is a primary folder. But if I store A as a subfolder of B, in turn a subfolder of C, and then in turn a subfolder of primary folder D, then Windows 10 might show wrong sizes of D and all the subfolders (since finally for A, the filenames inclusive of file paths would be too long). This also explains why the same folder might show the wrong size in my SSD Windows Drive C, but when copied into the Data Drive D it might show the correct size. This is because in Drive D it is a primary folder, but in Drive C you are already several steps down the "path" by the time you reach the "Documents" or "Pictures" folder.

Of course, the lengths of filenames won't help either. It is beyond me why some pictures, etc. I downloaded have filenames of over 50 characters.

The real solution has to be worked out by Microsoft, but based on the above, there is at least some way to avoid (NOT solve) the problem. (1) Avoid excessively long names for files and folders/subfolders. (2) More importantly, avoid too big a "tree" with numerous "branching" into more and more subdivisions into subfolders. I know this is a bit difficult to follow since most new computers nowadays have an SSD of 256GB or 512GB and some in addition a 1TB hard drive.

This problem is annoying because it appears sporadically and it applies to some but not all folders. Sometimes the file folders displayed are simply ridiculous. I am now using Windows 10 but if I remember correctly I encountered the same problem several times with Windows 8 in my old computer too. That computer had since broken down, and at that time I thought the wrong file sizes might be due to hard disk failure.

Now with my new HP computer using Windows 10, just now I copied some 3GB folder saved in a flash drive to Drive C (SSD) [There is also a Drive D - Hard drive]. The size of the copied folder in Drive C was shown as about 150 MB (yes, not GB) which was simply nonsensical. One single file in the folder can be 150MB already. The subfolder sizes were also wrong but file sizes seem to be right and the files can be opened. I even changed the name of the main folder but is still wrong folder size when copied. But when I copied instead into drive D, the folder size was correctly displayed. All the folder and subfolder sizes were displayed correctly in the original flash drive.

When I copied folders of some other flash drives onto Drive C (SSD), there was no problem either so far. As I said it is annoying because it occurs sporadically. Does anyone have any insight on the source of the problem, and any way to diagnose it? Thanks in advance.

I have the exact same problem on Windows 10 Home (Version 1803 (OS Build 17134.112)). Really annoying. Wrong calculation (like 150gb are missing!!!) for parent folder, and when I go into the folder and select the folders contained in it, it gives me a different total size, which is STILL inaccurate.