my ($Size)=( (qx{dir /s "$TargetPath"})[-2]=~ /([\d,]+) bytes/ );

##</code><code>##

my ($Size)=( (qx{dir /s "$TargetPath" | find "bytes" })[-2]=~ /([\d,]+) bytes/ );

##</code><code>##

use Win32::OLE;

my $size = Win32::OLE->CreateObject('Scripting.FileSystemObject')
    ->GetFolder( $TargetPath )
    ->size();

##</code><code>##

my (@dirs, @files) = ($TargetPath);
scalar map{ 
    push @{ (-d) ? \@dirs : \@files }, $_ 
} glob pop(@dirs) . '/*' while @dirs;
my $size += -s for @files;