In order to get a good quality A3 size print, what size do you ideally need the original image to be? For example, is 1 megabyte big enough? Is there even a rough image size requirement guide for different size prints ? Hope this makes sense
This website would seem to show that you'd need a file size of a minimum of 19.4 Mb for a 300dpi print based on a 11.69" x 16.53" (A3) size and scaling up to the next nearest size.
It could, but it still won’t be a sharp image. I’ve printed 5/6mb pictures at A3 which have been pretty sharp (depends on the printer quality too, of course).