<form action="" method="POST" >
Misli : <input type="text" name="misli" /> <br />
Oran : <input type="text" name="oran" /> <br />
<input type="submit" value="Gonder" name="noname" /> <br />
</form>
<?php
if($_POST){
$_POST['misli'] = str_replace(",",".",$_POST['misli']);
$_POST['oran'] = str_replace(",",".",$_POST['oran']);
$misli = (float)$_POST['misli'];
$oran = (float)$_POST['oran'];
$toplam = $misli*$oran;
echo $toplam;
}