If you have set Google as your default search provider, you can use the browser’s address bar as an instant calculator.
Simply enter the calculation in the address bar, Google will compute the answer on its own servers and will send you the result as a “search suggestion.” You don’t even have to press the Enter key.
This works with IE and Google Chrome while in the case of Firefox, you’ll have to type the expression in the browser’s search box instead of the address bar.
You can also perform calculations inside the browser offline without requiring Google.
Also see: Do More from your Browser’s Address Bar