Most laptops have it listed in the "Specs" table........it's a best guess, or an average in my opinion as I don't know how they calculate it and come up with a battery life number. Laptops these days would have to be at least 5-7+ depending on what kind you got. A gaming laptop will probably be less.....and an ultraportable energy efficient laptop will probably be more. Also, some come with standard batteries and some come with batteries with more cells. Look in the specs and that should give you a good idea of what you are getting into.