A convertor within Celestia (which actively changes km to RSun, etc.) would be more useful than having to manual type the number into the calculator. If all you need is to change units, there's a calculator for astronomical measurements at http://www.onlineconversion.com/astronomical.htm.
"I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able to rightly apprehend the kind of confusion of ideas that could provoke such a question."