First: I’ll preface this by saying that my status as an American is questionable. I don’t own any guns. I don’t have a huge SUV. I’ve never sued anyone. I’ve never watched a single reality TV show. My sense of entitlement is almost non-existent. I’m expecting the deportation proceedings to start any day. I just hope they send me to Canada. (Totally joking about all of that stuff… It is all true, but the tone is meant to be humorous.) 
Bike sizing is complicated. There are some basic things that you can figure out by talking to people, but a lot comes down to test riding and getting a feel for a bike. I’m 2″ taller and a little longer in the leg than you and I ride an XL in the Gary Fisher 29ers. That’s the most simple measurement. You get on the bike, adjust the saddle height, then get a feel for how comfy it is… how far you have to reach to get the bars… how much bend is in your back. Those are all subjective.
Personally, I’m an old roadie and I like my handlebars low and wide. My first move would be to lower the stem as far down as it can go… usually even turning it upside-down to get the bars at least 4″ lower than the saddle. Most humans don’t like that.
A good shop will be able to help you find the right size. I’d suggest that you ride a Large and an XL and get a feel for both. A good shop will actually allow you to ride the bike on a test ride in the manner that you’d actually use the bike. Many have demo days at local trails so that you can take the bike out on the trails and really get the feel for it. That often happens in the spring, rather than the fall. All shops will let you test ride.
I hope that is a good start.
PEte