ColdFusion Convert To Number

Pulling screen resolution with easy JavaScript Document Write. Using ColdFusion 9.0.

I can get proper numbers etc. But they are not "numbers" must be coming as text. As I cannot use as a number variable...

The code gets me: Available browser width: 1366 Available browser height: 728

And error of: The value document.write(screen.availWidth); cannot be converted to a number.

Any ideas of how to simply convert these to numbers I can work with... Without putting into a form and resubmitting through a form???

Thx

<cfset screenwidth = "<script>document.write(screen.width);</script>" > 
<cfset screenheight = "<script>document.write(screen.height);</script>" > 
<cfset availWidth = "<script>document.write(screen.availWidth);</script>" > 
<cfset availHeight = "<script>document.write(screen.availHeight);</script>"> 

<cfoutput> 
    <div style="padding:15px;"> 
    Available browser width: #availWidth#<br /> 
    Available browser height: #availHeight#<br /> 
    </div> 
</cfoutput> 

 <cfset nw = availWidth * 2>

  <cfset nh = availheight * 2>

  <cfoutput>#nw# and #nh#</cfoutput>