Size of Music Wire?

What number of "music wire" are you buying to make strings the equivalent of 10ga package strings?  What about 18 gauge plain package strings?  Those are the two I most commonly use for my dulcimer set up in Bagpipe Xxx.  Although I kinda like the look of black strings, the humid semi-salt air where I live really plays havoc with ordinary package strings, but doesn't seem to bother music wire strings so much.