7 day or 14?

Hello,
I'm travelling to Japan for two weeks and arriving in Osaka but I'm not sure if I need a 7 day or 14 day rail pass.

I plan to stay in Osaka/Kyoto/Nara and maybe Hiroshima for the first week and the second will be primarily spent in Tokyo city.
I'm a bit confused about the JR rail pass... Does it give me complete access to all the subway trains in Tokyo as well as the bullet trains? Or would i just need a metro pass or similar for my time in Tokyo.
Do I only need a 7 day pass to get me around Osaka/Kyoto etc and then into Tokyo whereupon it will be pretty much useless? Or a 14 day pass to get me around the whole country AND Tokyo city?

Hope that makes sense,
Brian :)