You can use Corpscon, a free downloadable conversion utility from the Army Corps of Engineers to run conversions for SPCS (State Plane), UTM, Lat., Long, etc. Not sure what you're trying to do but FWIW, it doesn't convert to or from WGS84 coordinate datums.
Be sure to download the appropriate Geoid file(s). Help is limited with this program but it's useful and it's free.
http://crunch.tec.army.mil/software/corpscon/corpscon.html#download
George