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Editorial Team
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Asked: 2026-05-24T22:22:12+00:00

I was wondering, what is the longest possible name length allowed by the Windows

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I was wondering, what is the longest possible name length allowed by the Windows kernel?

E.g.: I know the kernel uses UNICODE_STRING structures to hold all object paths, and since the byte length of a wide-character string is stored inside a USHORT, that allows for a maximum path length of 2^15 – 1 characters. Is there a similar, hard restriction on a file name (rather than path)? (I don’t care if NTFS or FAT32 imposes a particular restriction; I’m looking for the longest possible theoretically allowed name in the kernel, assuming no additional file system or shell restrictions.)

(Edit: For those wondering why this even matters, consider that normally, traversing a directory is achieved by FindFirstFile/FindNextFile calls, one call per file. Given the function named NtQueryDirectoryFile, which is the underlying system call and which returns multiple file names per call, it’s actually possible to take advantage of this maximum-length restriction on the path to make an extremely-fast directory traverser that uses solely the stack as a buffer. Now I’m trying to extend that concept, and I need to know the maximum size of a file name.)

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1 Answer

  1. Editorial Team

    Ah, I found this page myself that guarantees that file names can’t be longer than 255 characters:

    • A pathname MUST be no more than 32,760 characters in length.
      …
    • Each pathname component MUST be no more than 255 characters in length.

    Which makes me wonder:

    Why does Windows use ULONGs for file name lengths, when it uses USHORTs for path lengths?!

    If anyone knows why this is, please post/comment! I’m rather curious. 🙂

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