Displaying File Size, But in Problem... HELP!

I am using this code to display file size in my theme and trying to get the file url from a custom field but its not working with full url it only need path, can any one tell me how can I use this with full url ?
 WORKING

<?php echo filesize('wp-content/uploads/insurance-quotes-595x286.jpg'); ?> bytes

PHP:

 NOT WORKING

<?php echo filesize('http://www.digmlm.com/wp-content/uploads/insurance-quotes-595x286.jpg'); ?> bytes

PHP:

IF POSSIBLE ALSO TELL HOW TO DISPLAY IN 'Mbs' INSTEAD OF BYTES

 

I found this solution BUT its not working with custom field Please help:-

ORIGINAL CODE

<?php
$remoteFile = 'http://us.php.net/get/php-5.2.10.tar.bz2/from/this/mirror';
$ch = curl_init($remoteFile);
curl_setopt($ch, CURLOPT_NOBODY, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true); //not necessary unless the file redirects (like the PHP example we're using here)
$data = curl_exec($ch);
curl_close($ch);
if ($data === false) {
  echo 'cURL failed';
  exit;
}

$contentLength = 'unknown';
$status = 'unknown';
if (preg_match('/^HTTP\/1\.[01] (\d\d\d)/', $data, $matches)) {
  $status = (int)$matches[1];
}
if (preg_match('/Content-Length: (\d+)/', $data, $matches)) {
  $contentLength = (int)$matches[1];
}

echo 'HTTP Status: ' . $status . "\n";
echo 'Content-Length: ' . $contentLength;
?>

PHP:

I MODIFIED THE CODE:-

<?php
$remoteFile = '<?php $values = get_post_custom_values("audio"); echo $values[0]; ?>';
$ch = curl_init($remoteFile);
curl_setopt($ch, CURLOPT_NOBODY, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true); //not necessary unless the file redirects (like the PHP example we're using here)
$data = curl_exec($ch);
curl_close($ch);
if ($data === false) {
  echo 'cURL failed';
  exit;
}

$contentLength = 'unknown';
$status = 'unknown';
if (preg_match('/^HTTP\/1\.[01] (\d\d\d)/', $data, $matches)) {
  $status = (int)$matches[1];
}
if (preg_match('/Content-Length: (\d+)/', $data, $matches)) {
  $contentLength = (int)$matches[1];
}

echo 'HTTP Status: ' . $status . "\n";
echo 'Content-Length: ' . $contentLength;
?>

PHP:

I Found this here http://php.net/manual/en/function.filesize.php