Manga News: Check out these new manga (5/18/15 - 5/24/15).
New Forums: Visit the new forums for Boku no Hero Academia!
Forum News: Cast your votes to determine the best parent in the Anime Showdown.
40 inch is plenty for a bedroom( larger than I'd want though), you don't need much bigger than that imo. I have a 42" for my living room and that's big enough for me. If you can get a 36" with better specs than a 40, I'd do so but yeah, 40 is big enough for a bedroom.
Although bigger TVs are recommended to perceive all the details in high resolutions, another factor to consider is that they may tire your eyes easily and give you headaches in the long run, I agree with goldb that 40'' is more than enough.
It's really dependent upon how big your room is etc. but generally speaking a 40" for a personal space is more than enough. Go into a store, look at the various models, make sure the one you want is 1080p, and you should be good to go.
A 40" is enough, any more bigger than that and you'll suffer headaches.
It depends on how far away from your room you are. Luckily science has the answer (or if not science whoever came up with this).