From the mailing list:

I've noticed that screen doesn't implement a potentially useful escape sequence that allows the client to query the window size.  (At least not in 4.0.2, which is the latest release version on the ftp site.)  I'm not sure how standard this sequence is, but it's implemented by xterm, dtterm, gnome terminal, and probably others.

I added support to my local copy by adding a few lines to ansi.c.  In case anyone is interested, I've attached the patch.

One reference I've found for this "CSI 18 ; t" sequence is here:
http://rtfm.etla.org/xterm/ctlseq.html#CSI%20Ps%20;%20Ps%20;%20Ps%20t

David

diff -Nru screen-4.0.2.orig/ansi.c screen-4.0.2/ansi.c
--- screen-4.0.2.orig/ansi.c        2003-12-05 06:57:05.000000000 -0700
+++ screen-4.0.2/ansi.c        2008-06-26 22:25:26.000000000 -0600
@@ -1225,6 +1225,11 @@
           SaveCursor();
           break;
         case 't':
+          if (a1 == 18) {
+            /* report the window size */
+            Report("\033[8;%d;%dt", curr->w_height, curr->w_width);
+            break;
+          }
           if (a1 != 8)
             break;
           a1 = curr->w_args[2];

(In answer to the question of "how standard"; it couldn't be officially standard, as t (7/5) falls under the "Private Use" final bytes for CSI sequences. -mjc)