NOT KNOWN DETAILS ABOUT FLYER PRINTING

I'm more than happy with my 1st order of flyers from printingcenterusa.com. They were encouraged by a buddy who's got employed them, and I am happy!I just have an issue about how to buy on the platform. Exactly what is the measurement of the A5 doc (half of an A4) on the platform? I wish to purchase a double sided flyer. I would like to confirm tha