based on screen size set the iframe width and height code example
Example 1: full width and height iframe
<body style="margin:0px;padding:0px;overflow:hidden">
<iframe src="http://www.youraddress.com" frameborder="0" style="overflow:hidden;overflow-x:hidden;overflow-y:hidden;height:100%;width:100%;position:absolute;top:0px;left:0px;right:0px;bottom:0px" height="100%" width="100%"></iframe>
</body>
Example 2: set iframe height and width
#IFRAME_ID {
width: 100%!important;
height: 100%!important;
}
<iframe src="http://www.youraddress.com" id="IFRAME_ID"></iframe>