or

var Mytab;function OnClientLoad(sender){ Mytab = sender; var scrW = screen.width; var scrH = screen.height; var val; if (scrW <= 1024){ val = "150px"; }else{ val = "300px"; } for (var i = 0; i < Mytab.get_allTabs().length; i++) { Mytab.get_allTabs()[i].width = val; }}<telerik:RadTabStrip ID="MyTab" runat="server" EnableEmbeddedSkins="False" OnClientLoad="OnClientLoad" .....<add path="Telerik.ReportViewer.axd" verb="*" type="Telerik.ReportViewer.WebForms.HttpHandler" validate="false" />