The Exoplanet Calcultor includes functions that are useful related to the study of planets outside of our solar-system (exoplanets). It also includes some functions generally useful for astronomy, since that's usually the discipline involved in studying exoplanets in the first place.
When dealing with extra-solar planet data there are several calculations you need to perform. The units can be tricky! Also, there are the pesky constants (Newton's Universal Gravitation constant, pi, and all that). These equations are worked out here to make it easier to do the math and handling the various units without pulling out all your hair.
The value above is in light-years (ly). However, this can be automatically converted to other distance units including parsecs, megaparsecs and kilolight-years.