You can convert your Counter-Strike sensitivity to the corresponding sensitivity in Overwatch. Since April 6th 2016 sensitivity in Overwatch is linear and very easy to calculate accurately.
PSA! Blizzard are still working on making you able to adjust your sensitivity in fractions, currently you can only change your sensitivity in integers (1, 2, 3 etc)
Does your Counter-Strike sensitivity convert into a fraction? The work around to this is
to either use the closest whole number or change your Counter-Strike sensitivity to
match the closest whole number in Overwatch.
This number is shown in brackets, for example [1.2].