Is UX the same as Usability?
What is the difference between web usability and Web user experience and their connection to each other
Read example and explanation here http://www.uie.com/brainsparks/2007/03/16/the-difference-between-usability-and-user-experience/
Usability answers the question "Is the user able to use the design and achieve his goal with minimum time taken, minimum training time and 100% success"
User Experience answers the question "How does the user feel when he starts interacting with the design and the time when he leaves it."
In other words, User experience is a broad form of practice which has USABILITY as a part in it.
So if we consider a UI Design, the design, the layout, the wordings, the placement of every component determines how the user experience will be. It will decide whether the user is delighted and will come back and spread good words abt the site.
Usability is more abt if the user is coming is he able to perform the task for which he is coming and accomplish the task in minimum time and max success rate.
Remember, a bad look and feel can have good usability but less User experience output. But if a user experience is high, the chances of usability being low is less.