How to set width of cfgid in percentage?

Then you have to find a way to get the browser to send information about screen size to ColdFusion. One way to do it is by means of AJAX. Another, in my opinion much simpler way, is to get Javascript to store the screen size as a cookie, and then to get ColdFusion to read the cookie. I was thinking of something like this

<script type="text/javascript">

var browserWidth = screen.width;

var browserHeight = screen.height;

var expiryDate=new Date();

/*set expiry date tomorrow*/

expiryDate.setDate(expiryDate.getDate()+1);

document.cookie= 'browserWidth='+browserWidth+',browserHeight='+

                            browserHeight+',expires='+expiryDate;

</script>

<cfset percentWidth = 90>

<cfif isDefined("cookie.browserWidth")>

    <cfset browserWidth = cookie.browserWidth>

<cfelse>

    <cfset browserWidth = 800>

</cfif>

<cfset gridWidth = int(percentWidth*browserWidth/100)>

<cfform>

<cfgrid format="html" name = "myGrid" width="#gridWidth#">

</cfgrid> 

</cfform>