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I'm guessing there's no hard limit, but I know that performance degrades when you put too many files into a single Windows folder. Does anybody have any good rules of thumb for when it becomes noticeably slow to open a file?

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Assuming NTFS here, in which case the technical limit is around 4 billion files. And until you go over 10s of thousands per directory you really should not worry too much.

Note however that programs like Explorer suffer much sooner than 10s of thousands, because they try to access all files in a given directory to get meta-data, etc.

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    In my testing here on Win 7 Explorer is actually faster than some other tools that allegedly are more efficient.
    – Joey
    Jul 16, 2009 at 23:44
  • I haven't played with Win 7 yet, but mainly for lack of time and a good machine. I'm glad they appear to have invested some time in improving Explorer then.
    – jerryjvl
    Jul 16, 2009 at 23:49
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Opening a file won't be very slow regardless of how many files you have in a folder. What certainly is going to kill you is enumerating files in that folder. So taking a look at the contents of that folder with Explorer, Far, dir, Get-ChildItem, whatever.

That being said, I have around 2.5k files and folders in my temp folder and display is instantaneous, so that's apparently still a small number.

ETA: Ok, just tried it, 10000 files in a folder take around one second to open that folder in Far, this and 20000 files don't even matter in Explorer.

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    Just wait until you start doing that over a network. A couple apps I have to maintain like to archive everything in the same place: 100,000 or more files. Don't even think about opening that folder in explorer.
    – Joel Coehoorn
    Jul 16, 2009 at 22:48
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    Ok, agreed there. For local folders it doesn't matter apparently, I just let my copy nul %i run to 100k and Explorer takes about 1 second to open that folder, sorting the files takes a fraction of a second longer.
    – Joey
    Jul 16, 2009 at 22:52
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    @JoelCoehoorn: SMBv2 worked wonders on our machines.
    – surfasb
    Nov 30, 2011 at 20:58
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Look here. It says for files per volume, not per folder.

  • NTFS: 2^32 - 1 = 4.294.967.295 files
  • FAT: Approximately 4 million
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For a decent consumer grade hardware, 150K files per folder is the number I have come across as per Windows 10 build 18362.356 using its native Explorer on a WD Blue 4TB hard disk drive in NTFS (partitioned 2 TB + 2TB ). For all files at fixed size of 24KB and filetype .7z . 150K is the number of files the explorer can display, I can select and do some operation. Any larger in the same folder and the windows explorer starts crawling.

It's highly likely this number is dependent on the File Explorer, filesystem, OS, drive speed, drive type (SSD/HDD/Raid HDD etc.) and also the supporting hardware itself like the Storage controllers, CPU and health of the SATA cables (or PATA or m.2 socket). For exammple the SouthBridge controllers would probably have a slower performance than CPU/NB controllers and connecting the drive to the SB should be a slower performance overall. Also 7zip's file explorer is much faster than Windows File Explorer in selecting huge number of files, in the range on 100Ks. I am not certain about the file sizes and if they will or won't affect the read time but my other folders with 1000s of images per folder take a long time, is it due to them having filetype of .jpg/.png etc. or is it due to their huge sizes or is it due to the explorer trying to generate thumbnails for them I am not sure. I have seen windows skips generating thumbnails for images >20 MB so that can be a valid concern.

If you want to be on the performant side, having about 50K files per folder in my opinion would be better as you wouldn't need to worry about different explorer's or os' etc. causing the file explorer to crash or take minutes of selection/display time.

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update 2021: as stated somewhere around 4 billion according to MS, I have tested with 1,8 million files in one dir on Windows 10, Win-Explorer scrolling and opening a random file was as fast as 1 file in a directrory

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    It was so long ago that I asked this question, I no longer have access to the system that had the problem or remember how many files I had. But I assure you it was a lot less than 4 billion.
    – Mark Ransom
    Mar 7, 2021 at 0:45
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    Thank you very much for the data point (if you're still there :) ), actually trying such extremes doesn't happen frequently.
    – Sz.
    Jan 10, 2022 at 12:38
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I had trouble some years ago with a directory which had about 30000 files, and new files couldn't be written (it was the "temp" directory of eMule...), it was on a FAT32 partition, but it's possible that I was using Win98 at the time, and that it was a limit of the OS itself.

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  • 32767 is a special number because it's the maximum that representation in a 16-bit signed value; "about 30000" is close enough.
    – Mark Ransom
    Jul 26, 2011 at 18:57
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I use Windows 10, and 25,000 images in one folder (average size of the file is 500 KB took more than an hour to load completely in the folder. The suggested number of files in one folder is 5000.

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  • What does "load" entail? This sounds like the time it takes to copy that many files to a folder.
    – MatthewMartin
    Jan 25, 2022 at 17:26
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It depends on the file system. NTFS is way better than FAT32. FAT32 has a hard limit. However, the rule of thumb I go by is about 500 per directory.

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    I have image folders with several thousand images in a single directory, and audio folders with even more. 500 is a very very low limit for a windows folder.
    – TheTXI
    Jul 16, 2009 at 22:38

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