not sure how tall you are as the only thing i ever measure in CM is skis and i know how long they are just by sizing them up (i.e. i'm a Cali kid, so we measure everything in feet and inches, in terms of height).
at any rate, here's a good general guide to sizing:http://www.skis.com/guides/guide_skis.html
beyond that the best thing to do is to demo a few different sizes in a few different skis. every ski will ski differently. some skis ski short (i.e. they feel a lot shorter than their designated length) while other skis ski long (i.e. they feel a lot longer than their designated length).
the only real way to tell is to get out on some different sizes and see what fits.
another "general" rule of thumb was to deduct 10-15cm from the length of unshaped skis you used to ride. So if you were on a 198cm ski then the "general" rule of thumb would be to try between a 180 and 188 length in shaped skis.
of course, again, these are all just general guidelines and won't compare to actually trying out some different sizes on the slope.