<?php
// connect and login to FTP server
$ftp_server = "ftp.example.com";
$ftp_conn = ftp_connect($ftp_server) or die("Could not connect to $ftp_server");
$login = ftp_login($ftp_conn, $ftp_username, $ftp_userpass);

$file = "serverfile.txt";

// get size of $file
$fsize = ftp_size($ftp_conn, $file);
if ($fsize != -1)
  {
  echo "$file is $fsize bytes.";
  }
else
  {
  echo "Error getting file size.";
  }

// close connection
ftp_close($ftp_conn);
?>