Debido a que estuve bastantes visitas en mi versión wxWidgets del conversor de Celsius a Fahrenheit, decidí preparar una versión online que permita realizar fácilmente la conversión.

Convert Celsius to Fahrenheit Online está liberado bajo la licencia GNU GPL v3…

Acá está el código fuente completo:

<script type="text/javascript">
// *****************************************************************************
// Description: Convertir de Celsius a Fahrenheit Online by NeoEGM
// Author: Ezequiel Miravalles
// Last modification: 16/08/2009
// URL: http://www.neoegm.com/es/tech/online-tools/convert-celsius-to-fahrenheit-online/
// *****************************************************************************

/*******************************************************************************
	Copyright (C) 2009 Ezequiel Gastón Miravalles

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
*******************************************************************************/

function isNumber(x)
{ 
  return ( (typeof x === typeof 1) && (null !== x) && isFinite(x) );	//From http://snippets.dzone.com/posts/show/6937
}

function Round(number, digits)
{
	return Math.round(number * Math.pow(10,digits)) / Math.pow(10, digits);
}

function CelsiusToFahrenheit(celsius, fahrenheit)
{
	var num = celsius.value;
	
	if (num == "" || !isNumber(Number(num)))
		alert("Por favor ingresar un número");
	else
		fahrenheit.value=Round((9/5)*num+32, 2);
}

function FahrenheitToCelsius(fahrenheit, celsius)
{
	var num = fahrenheit.value;
	
	if (num == "" || !isNumber(Number(num)))
		alert("Por favor ingresar un número");
	else
		celsius.value=Round((5/9)*(num-32), 2);
}
</script>

<table>
<tr>
<td>Celsius:</td>
<td><input type="text" name="celsius_field" id="celsius_field" style="width:100px" /></td>
<td><input type="button" value="A Fahrenheit" onclick="CelsiusToFahrenheit($('celsius_field'), $('fahrenheit_field'))" /></td>
</tr>
<tr>
<td>Fahrenheit:</td>
<td><input type="text" name="fahrenheit_field" id="fahrenheit_field" style="width:100px" /></td>
<td><input type="button" value="A Celsius" onclick="FahrenheitToCelsius($('fahrenheit_field'), $('celsius_field'))" /></td>
</tr>
</table>