How to Print a Report made in Web Page

First of all insert the printable area into a Div.

then write below code in Page load

Suppose your Print button Id = btnPrint and
div id = printdiv

btnPrint.Attributes.Add("Onclick", "javascript:CallPrint('printdiv');");

pass this div id to the javascipt function written in HTML

function CallPrint(strid)
{
var prtContent = document.getElementById(strid);
var WinPrint = window.open('','','letf=0,top=0,width=1000,height=1000,toolbar=0,scrollbars=0,status=0');
WinPrint.document.write(prtContent.innerHTML);
WinPrint.document.close();
WinPrint.focus();
WinPrint.print();
WinPrint.close();
prtContent.innerHTML=strOldOne;
}