root/plugins/sfPropelFileStoragePlugin/lib/helper/PropelFileStorageHelper.php

<?php

/* Thanks to: http://www.php.net/manual/en/function.filesize.php#64387 */
function parse_file_size($size)
{
  /*
  Returns a human readable size
  */
  $i=0;
  $iec = array("B", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB");
  while (($size/1024)>1) {
   $size=$size/1024;
   $i++;
  }

  return substr($size,0,strpos($size,'.')+4).' '.$iec[$i];
}