<?PHP 
function diskUsage( $dir ) {    
    if ( is_file ( $dir ) )
        return filesize( $dir );        
    if( strlen( $dir ) - 1 != '\\' || strlen( $dir ) - 1 != '/' )
        $dir .= '/';        
    $handle = @opendir( $dir );    
    if( !$handle )
        return false;        
    while ( ( $file = readdir( $handle ) ) !== false ) {        
        if( $file != '.' && $file != '..' ) {            
            $use += diskUsage( $dir.$file );            
        }      
    }    
    closedir( $handle );
      return $use;
}
?>
// Anwendungsbeispiel
<?PHP
echo 'Speicherbelegung: ' . diskUsage("c:\\Temp") . ' Bytes';
?>