CALCULO W

<meta charset="utf-8">
<title> Calculo de W </title>
<form action="#" method="post">
    Watts: <input type="number" name="watt" required>
    <br>
    Valor KWH: <input type="text" name="kwh" required>
    <br>
    Horas : <input type="text" name="hr" required>
    <br>
    Dias : <input type="text" name="dia" required>
    <input type="submit" value="Calcular">
    <br>
    Inserir o valor do KWH usando "." ponto<br>
    EX: Preço do KWH cobrado em Jacareí-SP R$ 0.77702703
    <br>
    <a href="http://outervision.com/power-supply-calculator" target="_BLANK"> Power Supplay Calculator </a>
</form>
<?php
    if (empty($_POST["watt"])) {
        echo "";
    }
    else {
        $watt = $_POST["watt"];
        $kwh = $_POST["kwh"];
        $hr = $_POST["hr"];
        $dia = $_POST["dia"];

        $potencia = $watt * $hr * $dia / 1000;
        $valor_final = $potencia * $kwh;


        echo "

        <ul>
            <li>KWH: $potencia</li>
            <li>$dia Dia(as) ligado por $hr Hora(as) = R$ $valor_final</li>
        </ul>
            ";
        /*
            P = Potencia
G = KWH
H = Horas
D = Dias

G = P x H x D / 1000

G x Valor KWH = Valor em R$
        */
    }
?>