I need to find out the "Allocation Unit Size" selected when a particular hard-disk was formatted.

It doesn't appear in the properties information for the drive.

Is there any easy way to get this information?

3 Answers 3


Use the fsutil command:

fsutil fsinfo ntfsinfo [drive letter]

You'll have to run this command with administrator privileges.

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Now that powershell has caught up and has fledged out a little bit you can run this code in a powershell window:

Get-Volume | Format-List AllocationUnitSize, FileSystemLabel


you don't have to go through all that. make a .txt file with 1 character in it so it isn't 0 bytes, then copy it to the drive. when you look at properties it will have a "size on disk" which you will find is the allocation unit size, because that's the smallest amount it can occupy.

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