codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script language="javascript">
function Calcola(){
var l = document.getElementById('l').value.replace(',','.');
var h = document.getElementById('h').value.replace(',','.');
var tot = (h*l*250)
document.getElementById('calcolo').value=tot.toFixed(2);
}
</script>
<title>Documento senza titolo</title>
</head>
<body>
<form action="" method="get">
<input name="h" type="text" id="h" onkeyup="Calcola()" />
<input name="l" type="text" id="l" onkeyup="Calcola()" />
<input name="colcolo" type="text" id="calcolo" readonly="true"/>
</form>
</body>
</html>