You will never get the exact time on how your battery will last.
Since you have a 2011 Macbook Pro - do not even attempt to Calibrate your battery (unless you want to mess up your Macbook and your battery).
Normal usage is to keep your Macbook plugged in when close to a power outlet.
Once in a while, use it under it's own power and charge it back up once you're down to 75% to keep your battery in optimal condition.
Using your Macbook until the battery fully discharge may do more harm than good to your Macbook - search this forum and you'll see people having issues with their Macbook after they've let their battery rundown all the way to 0%.
From Apple's website.
Portables with built-in batteries
Current Apple portable computer batteries are pre-calibrated and do not require the calibration procedure outlined in this article. These computers use batteries that should be replaced only by an Apple Authorized Service Provider.
system preferences - users and groups - login items - if you see any apps there and you don't need it, delete them....
turn your bluetooth off if you're not using it.
turn off automatic brightness
turn off infrared remote receiver if you're not using an apple remote.
keep your brightness at 50%
open activity monitor - under all processes - see what's using around 10% in the %CPU section.
if you don't need it highlight it and hit quit process...
doing the above might increase the life of your battery to 5+ hours..
Ok... I know this is coming after sometime... I've noticed a weird thing... When I startup my computer I have "Stickies" and "Opus Domini Lite" start up... I also have Sophos installed so it runs in the background... The battery indicator says 4-5 hours when no programs other than these are open and when I open my browser, which is Chrome, the indicator goes from 6-7 hours... I find this strange... Any idea why this might be occuring?