[PowerShell] Get File Size on Disk

Get-FileSizeOnDisk.ps1

# Retrieves the size of a file on disk
#
# Adapted from Kim Doan's original script here: 
#  https://kimconnect.com/powershell-get-size-on-disk-of-files-in-windows/
#
# Note: This assumes that the filesystem type is NTFS
#       and that the cluster size is 4KB

[cmdletbinding()]
param(
    [parameter(ValueFromPipeline)]
    [ValidateNotNullOrEmpty()]
    [string]$file,
    [int32]$clusterSize=4096,
    $maximumSizeThreshold=604
)

add-type -type  @'
using System;
using System.Runtime.InteropServices;
using System.ComponentModel;
using System.IO;

namespace Win32Storage
{
  public class ExtendedFileInfo
  {    
    public static long GetFileSizeOnDisk(string file)
    {
        FileInfo info = new FileInfo(file);
        uint dummy, sectorsPerCluster, bytesPerSector;
        int result = GetDiskFreeSpaceW(info.Directory.Root.FullName, out sectorsPerCluster, out bytesPerSector, out dummy, out dummy);
        if (result == 0) throw new Win32Exception();
        uint clusterSize = sectorsPerCluster * bytesPerSector;
        uint hosize;
        uint losize = GetCompressedFileSizeW(file, out hosize);
        long size;
        size = (long)hosize << 32 | losize;
        return size;
    }

    [DllImport("kernel32.dll")]
    static extern uint GetCompressedFileSizeW([In, MarshalAs(UnmanagedType.LPWStr)] string lpFileName,
       [Out, MarshalAs(UnmanagedType.U4)] out uint lpFileSizeHigh);

    [DllImport("kernel32.dll", SetLastError = true, PreserveSig = true)]
    static extern int GetDiskFreeSpaceW([In, MarshalAs(UnmanagedType.LPWStr)] string lpRootPathName,
       out uint lpSectorsPerCluster, out uint lpBytesPerSector, out uint lpNumberOfFreeClusters,
       out uint lpTotalNumberOfClusters);  
  }
}
'@
function Get-FileSizeOnDisk{
    param(
        [parameter(ValueFromPipeline)]
        [ValidateNotNullOrEmpty()]
        [string]$file,
        [int32]$clusterSize=4096,
        $maximumSizeThreshold=604
    )
    # At this time, it's unclear as to what minimum size a file should be so that Windows would compact it into NTFS MFT record,
    # so that there's no wastage of 1 cluster extent;
    # The range of values seem to be from 539 to 604 bytes
    [int]$minimumSizeThreshold=539
    #[Double]$size=$(try{get-item "$file"}catch{}).Length
    [Double]$size=[Win32Storage.ExtendedFileInfo]::GetFileSizeOnDisk($file)
    [int]$sizeOnDisk=0;

    if ($size -le $minimumSizeThreshold){
        $sizeOnDisk=0;
        }else{
            if ($size -lt $maximumSizeThreshold){
                $sizeOnDisk=(($size-$minimumSizeThreshold)/($maximumSizeThreshold-$minimumSizeThreshold))*$clusterSize
                } # This is a blind guess probability that file on disk is equal to cluster size
            else{
                [int]$remainder=$size%$clusterSize
                if ($remainder -eq 0){
                        $sizeOnDisk=$size
                    }else{
                        $sizeOnDisk=$size-$remainder+$clusterSize;
                        }
                }
            }
    
    #if($size -ge 538 -and $size -lt 542){write-host $file}
    return $sizeOnDisk
}

Get-FileSizeOnDisk -file $file -clusterSize $clusterSize -maximumSizeThreshold $maximumSizeThreshold