As I am writing the sequel to Us & Them, I often have to do some math. Nothing complex, I just aim at having a coherent sequence of events that map well to space, time, and speed.
Google, unlike other search engines, is capable of doing relatively complex calculations in units like AU, light days, etc.
At a certain level, however, Google gives up an does not provide a meaningful result:
(((8*30*24*60*60*150000 km) + (21 light days) + 1 light year) in light years
Even limited as it is, it’s still a handy tool for basic calculations.