...
my $height = $mw->screenheight;
my $width  = $mw->screenwidth;

my $geom = $mw->geometry;

$mw->title("New Title ($geom)");

##</code><code>##

my $height = $mw->height;
my $width  = $mw->width;

$mw->title("New Title ($width x $height)");