<div style="width:1cm;" id="wallpaper"></div>
<SCRIPT LANGUAGE="JavaScript">
document.write('Your screen resolution is set at:\n' + screen.width + ' x ' + screen.height + ' pixels<br/>');
var ww = document.getElementById("wallpaper").offsetWidth, w = screen.width/ww, h = screen.height/ww, r = Math.round(Math.sqrt(w*w + h*h) / 2.54);
document.write('Your monitor size:\n' + (screen.width/ww).toFixed(1) + ' x ' + (screen.height/ww).toFixed(1) + ' cm, '+ r +' Inch<br/>');
</SCRIPT>