diff --git a/admin/include/functions.php b/admin/include/functions.php
index 3d8ffa756..f587c3028 100644
--- a/admin/include/functions.php
+++ b/admin/include/functions.php
@@ -625,6 +625,28 @@ function get_fs_directories($path, $recursive = true)
   return $dirs;
 }
 
+/**
+ * returns the size (in bytes) of a filesystem directory
+ *
+ * @since 11
+ * @param string path
+ * @return int
+ */
+function get_fs_directory_size($path)
+{
+  $bytestotal = 0;
+  $path = realpath($path);
+
+  if ($path !== false && $path != '' && file_exists($path))
+  {
+    foreach (new RecursiveIteratorIterator(new RecursiveDirectoryIterator($path, FilesystemIterator::SKIP_DOTS)) as $object)
+    {
+      $bytestotal += $object->getSize();
+    }
+  }
+  return $bytestotal;
+}
+
 /**
  * save the rank depending on given categories order
  *
diff --git a/admin/intro.php b/admin/intro.php
index 987491eda..a3bb94f44 100644
--- a/admin/intro.php
+++ b/admin/intro.php
@@ -388,15 +388,22 @@ if (isset($result[0]['SUM(filesize)']))
   $data_storage['Formats'] = $result[0]['SUM(filesize)'];
 }
 
-//If the host is not windows, get the cache size
-if (strtoupper(substr(PHP_OS, 0, 3)) !== 'WIN') 
+// PHP 5.5.19 is the oldest version get_fs_directory_size was tested on
+if (version_compare(PHP_VERSION, '5.5.19') >= 0)
 {
-  $f = './_data';
-  $io = popen ( '/usr/bin/du -sk ' . $f, 'r' );
-  $size = fgets ($io, 4096);
-  $size = substr ( $size, 0, strpos ( $size, "\t" ) );
-  pclose ( $io );
-  $data_storage['Cache'] = $size;
+  if (!isset($_SESSION['cachedir_info']) or $_SESSION['cachedir_info']['calculated_on'] < strtotime('5 minutes ago'))
+  {
+    $start_time = get_moment();
+
+    $_SESSION['cachedir_info'] = array(
+      'size' => get_fs_directory_size($conf['data_location']),
+      'calculated_on' => time(),
+    );
+
+    $logger->debug('[admin/intro::'.__LINE__.'] cache size calculated in '.get_elapsed_time($start_time, get_moment()).' ('.$_SESSION['cachedir_info']['size'].' bytes)');
+ }
+
+  $data_storage['Cache'] = $_SESSION['cachedir_info']['size'] / 1000;
 }
 
 //Calculate total storage