ทำการ count input เฉพาะ input ที่มีการกรอกข้อมูลครับ

count(array_filter($_POST["to_more"]));

<?php
    if(isset($_POST["submit"]))
    {
     $c = 0;
     foreach($_POST["to_more"] as $single)
          if(!empty($single) || $single !== "") ++$c;
     echo $c;
    }
?>
<form name="f1" method="post">
<input type="text" name="to_more[]">
<input type="text" name="to_more[]">
<input type="text" name="to_more[]">
<input type="submit" name="submit" value="OK">
</form>

<?php
    function notempty($val){
         return !empty($val);
    }

    if(isset($_POST["submit"]))
    {
     echo count(array_filter($_POST["to_more"],"notempty"));
    }
?>
<form name="f1" method="post">
<input type="text" name="to_more[]">
<input type="text" name="to_more[]">
<input type="text" name="to_more[]">
<input type="submit" name="submit" value="OK">
</form>

$to_more = array("","second","third","","");
function notempty($val){
         return !empty($val);
}

echo count(array_filter($to_more,"notempty"));