hi
excel provides most of the standard print sizes but not all mainly becasue
of all of the different kinds of printers available.
on the page setup dialog box, click the options button. this should deplay
the setting of your default printer. it should have a selection list of sizes
it can print in. if A3 is not there, then it may not be available. if you
have more than one printer, try switching default printers and check that
printer.
Regards
FSt1