Eradicator

I've used the ones at http://www.gpsvisualizer.com/calculators before. Some combination of the calculators on that page will do what you want.

You need to sign the logbook in order to log it online. It's a simple rule, why people find it so hard to understand? If you haven't signed the logbook, and you claim the find online, you're cheating. It doesn't matter if you have seen the cache or someone signing it. Unless you've signed the logbook yourself, claiming you have found is the same as fromleaping or armchair logging. Hmm. I guess I'm a cheater then. I don't see much point in signing the log, but I also don't log a find unless I have the cache container in hand. I'll usually open it up so I can note if the contents are wet or otherwise damaged, but then just seal it back up, return it to its spot, and continue on my merry way. If the CO has an issue with that sort of log, so be it.

The fact that the app requires you to leave a comment to log a find makes this sort of thing inevitable. With a straightforward cache, there's not always something pithy to be said.