title_body: What page size maximizes readability across common ebook readers? Suppose that I have to create a PDF ebook (meaning no automatic word reflow, etc). What page size (width by height) maximizes readability across common e-readers and mobile devices? 
  
  Context: I typically create my ebooks using LaTeX, meaning that the PDF format is the only option I have easy access to. It's possible to design for multiple form factors, but each additional form factor requires additional debugging (in the form of looking for overfull/underfull hboxes, hyphenation issues, etc.), which is why I would prefer to work with only one form factor.
upvoted_answer: This would be extremely difficult since the broad range of devices out there have vastly different physical screen sizes and aspect ratios. Your best bet would be to use a small page size (perhaps 4" x 3") so that users with e-book apps on their smartphones would still be able to comfortably read the text. This comes at a price: e-book readers or tables with large screens will display very large text - although some might allow you to zoom out or display multiple pages at a time.
  
  I would suggest a slightly different route based on this similar question. Instead of exporting from LaTeX to PDF, export to HTML. Then use a tool such as Calibre to convert the HTML files produced to a MOBI or EPUB file.