Hangul vs. Roman

Hangul is the Korean writing system. Roman is the Western writing system. And both are used for the Korean language and the conversion between the two systems is called Romanization.

Wikipedia has a good primer on this topic and there's a quick reference table at Tour2Korea but the process is fairly simple enough to be explain as a table loop-up process. And since it can be explained as a table look-up that means that some computer can do this conversion automatically. And since some computer can do this conversion automatically, that means that it can be found somewhere on the internet.

And it is, courtesy of Sori.org.

Alternatively, there's also the Roman to Hangul & Hangul to Roman converters at Kawa.net.