I didn't even think to put the measurements! Thank you, from now on I will have to remember to add that information! It is 18"Wx15"H. The bottom has a 3"W surface, but the sides of the bag are sewn together without width.
I am also new... and do not know about postage. I will have to look around and see if I can find an answer, and if I find out, I will let you know! :-)