ASP.Net: Access client Screen Width and Height from code behind (Server Side)

Why this code doesn't work.

<script type="text/javascript">
    function SetName() {
        var label = document.getElementById("<%=Label24.ClientID %>");
 
        //Set the value of Label.
        label.innerHTML = screen.width;
 
        //Set the value of Label in Hidden Field.
        document.getElementById("<%=Label26.ClientID %>").value = label.innerHTML;
    }
</script>

<asp:Button ID="Button9" runat="server" Text="Creation" OnClientClick="SetName();" />

Label24.Text = Request.Form(Label26.UniqueID)
Dim wid = Label24.Text
mpe.X = wid - (wid / 4)
mpe.Show()

Did i miss something?