Displays the file size of a file in the local filesystem (relative to MODX_BASE_PATH) in bytes, kilobytes, or megabytes depending on its size.

filesize

<?php
$path = MODX_BASE_PATH . $file;
$fs =  filesize($path);

if ($fs < 1024) {
  return "${fs}B";
}
elseif ($fs < (1024*1024)) {
  return  round($fs / 1024, 0) .'KB';
}
elseif ($fs < 1073741824) {
        return round($fs / 1048576, 1) . 'MB';
}

This is just quick-and-dirty; assumes path is relative to MODX_BASE_PATH, and the unit descriptors are hard-coded. Adjust as necessary.