To know the limit, try uploading a file with the name “phpinfo.php” to your site, with this inside:

<?php
echo "Current PHP version: " . phpversion();
echo "<br/>*****<br/>";
phpinfo();
?>

Then visit the location of that file on your browser. On the page you will see all the information related with the PHP configs. You want to look for the line with post_max_size

If I’m not mistaken, that’s the limit.