Cartisan Maps site is now dead (domain name grabbed by someone else); however, I have uploaded the two files to MediaFire, and updated the links to the spreadsheets to point to these files. There also may be problems running this in Excel, as it seems to want a password for some functions; however, it runs fine on the free Office clone LibreOffice..
Cartisan Maps has several free spreadsheet tools for basic coordinate conversions; each one can handle up to 5000 sets of coordinates. Files are in Microsoft Excel format, but seem to work fine in OpenOffice 2.4.
Cartisan Map Coordinate Converter: Enter latitude and longitude in separate columns for degrees, minutes and seconds, and have them converted to a DD MM SS string, DD MM.d string, or numeric decimal degrees. The first column, labeled Hemisphere, is multiplied times the longitude, and if you leave it blank, the calculated degree value for longitude will always be zero. Enter “1” for East longitudes, “-1” for West longitudes, and make sure your longitude degree value is always positive; or, enter a “1”, and then enter positive and negative values for the longitude degree value.
Cartisan Total Map Coordinate Converter: Converts from decimal and DDMMSS latitude/longitude to UTM and MGRS, and back again; includes support for 14 datums, including NAD27 and WGS84. Also has another version of a converter from degrees/minutes/seconds to decimal degrees and back, similar in output to the one above.Requires that you have macros enabled in your spreadsheet program. Notes: 1. File is in the .RAR compression format; if your unzipping program can’t handle that, try 7-Zip. 2. Enter your coordinate data in the areas highlighted in green in the spreadsheet.