<script type="text/javascript">
function addEvent_imc(elm, evType, fn, useCapture)
{
// cross-browser event handling by Scott Andrew
if(elm.addEventListener)
{
elm.addEventListener(evType, fn, useCapture);
return true;
}
else if(elm.attachEvent)
{
var r = elm.attachEvent('on' + evType, fn);
return r;
}
else
{
elm['on' + evType] = fn;
}
}
function addListeners_imc(e)
{
if(!document.getElementById)
return;

var calcula_btn = document.getElementById('calcula_btn_imc');
addEvent_imc(calcula_btn, 'click', imc, false);
}
function imc(e)
{
var peso = parseFloat(document.getElementById('peso_imc').value);
var altura_m = parseFloat(document.getElementById('altura_m_imc').value);
var altura_cm = parseFloat(document.getElementById('altura_cm_imc').value);

var altura = (altura_m * 100 + altura_cm)/100;
var imc = peso/(altura*altura);

if(isNaN(imc))
{
alert('use apenas números para suas medidas');
return false;
}

imc = Math.round(imc*100)/100;
alert('Seu IMC é ' + imc);
}
addEvent_imc(window, 'load', addListeners_imc, false);
</script>

<form id="imc">
<table cellpadding="3" cellspacing="1" border="0" width="150" style="font-size:11px;font-family: arial;background-color:#fff;color:#fff">
<tr>
<th colspan="2" style="background-color:#fff;color:#f09;text-align:center;">Calculadora IMC</th>
</tr>
<tr>
<td style="background-color:#f09">Peso:</td>
<td style="background-color:#f09"><input type="text" id="peso_imc" style="font-size:11px;font-family:arial;width:25px" /> kgs</td>
</tr>
<tr>
<td style="background-color:#f09">Altura:</td>
<td style="background-color:#f09" nowrap="nowrap">
<input type="text" id="altura_m_imc" style="font-size:11px;font-family:arial;width:25px" /> m
<input type="text" id="altura_cm_imc" style="font-size:11px;font-family:arial;width:25px" /> cm
</td>
</tr>
<tr>
<td colspan="2" align="center" style="background-color:#f09">
<input type="button" value="calcular" id="calcula_btn_imc" style="font-size: 11px;font-family: arial;" /></td>
</tr>
<tr>
<td colspan="2" style="font-size:10px;" align="right"><a href="http://www.dietaesaude.org" target="_blank" style="color:#f09;">Dieta e Saude</a></td>
</tr>
</table>
</form>