I found this website to calculate it:

http://eehouse.org/fixin/formfmu.php

If I used my measures 46T x 16T - 16", suggest me a chainlengths of 48, so the links are 1/2" length I count the double, that's 96 chainlinks.
Please can anyone confirm this is true?, I don't speak english very well and some terms confuse me, thanks.