Muchas gracias por la pronta respuesta.
Como dije en un principio soy principiante en programacion, aqui te paso el codigo:
<!DOCTYPE HTML>
<html>
<title>FORMULARIO DE CUBICACION</title>
<head>
</head>
<body>
<h1 align='center'>FORMULARIO DE CUBICACION</h1>
<script>
function calcular(){
valorconst = 0.0514;
n1 = Number (document.cubi.n1.value);
n2 = Number (document.cubi.n2.value);
n3 = Number (document.cubi.n3.value);
n4 = Number (document.cubi.n4.value);
n5 = Number (document.cubi.n5.value);
n6 = Number (document.cubi.n6.value);
n7 = Number (document.cubi.n7.value);
n8 = Number (document.cubi.n8.value);
n9 = Number (document.cubi.n9.value);
n10 = Number (document.cubi.n10.value);
document.cubi.st1.value = (parseInt(n1) * parseInt(n1)) * parseInt(n2) * valorconst;
document.cubi.st2.value = (parseInt(n3) * parseInt(n3)) * parseInt(n4) * valorconst;
document.cubi.st3.value = (parseInt(n5) * parseInt(n5)) * parseInt(n6) * valorconst;
document.cubi.st4.value = (parseInt(n7) * parseInt(n7)) * parseInt(n8) * valorconst;
document.cubi.st5.value = (parseInt(n9) * parseInt(n9)) * parseInt(n10) * valorconst;
}
</script>
<form name="cubi">
<table border="1" align="center">
<tr>
<th>NUMERO</th>
<th>ESPECIE</th>
<th>DIAMETRO</th>
<th>LARGO</th>
<th>PIES</th>
</tr>
<!--Fila 01-->
<tr>
<th>1</th>
<th>
<select>
<option value="al">Almendrillo</option>
<option value="mr">Mara</option>
<option value="och">Ochoo</option>
</select>
</th>
<th><input type="text" name="n1" onkeyup="calcular();"/></th>
<th><input type="text" name="n2" onkeyup="calcular();"/></th>
<th><input type="text" name="st1" readonly="readonly"/></th>
</tr>
<!--Fila 02-->
<tr>
<th>2</th>
<th>
<select>
<option value="al">Almendrillo</option>
<option value="mr">Mara</option>
<option value="och">Ochoo</option>
</select>
</th>
<th><input type="text" name="n3" onkeyup="calcular();"/></th>
<th><input type="text" name="n4" onkeyup="calcular();"/></th>
<th><input type="text" name="st2" readonly="readonly"/></th>
</tr>
<!--Fila 03-->
<tr>
<th>3</th>
<th>
<select>
<option value="al">Almendrillo</option>
<option value="mr">Mara</option>
<option value="och">Ochoo</option>
</select>
</th>
<th><input type="text" name="n5" onkeyup="calcular();"/></th>
<th><input type="text" name="n6" onkeyup="calcular();"/></th>
<th><input type="text" name="st3" readonly="readonly"/></th>
</tr>
<!--Fila 04-->
<tr>
<th>4</th>
<th>
<select>
<option value="al">Almendrillo</option>
<option value="mr">Mara</option>
<option value="och">Ochoo</option>
</select>
</th>
<th><input type="text" name="n7" onkeyup="calcular();"/></th>
<th><input type="text" name="n8" onkeyup="calcular();"/></th>
<th><input type="text" name="st4" readonly="readonly"/></th>
</tr>
<!--Fila 05-->
<tr>
<th>5</th>
<th>
<select>
<option value="al">Almendrillo</option>
<option value="mr">Mara</option>
<option value="och">Ochoo</option>
</select>
</th>
<th><input type="text" name="n9" onkeyup="calcular();"/></th>
<th><input type="text" name="n10" onkeyup="calcular();"/></th>
<th><input type="text" name="st5" readonly="readonly"/></th>
</tr>
</table>
</form>
</body>
</html>
Me imagino que todo este codigo tu lo podrias simplificar de manera significativa haciendo uso de funciones, espero tu ayuda gracias.
