The new F-Gas regulation sets leak checking requirements based upon 5, 50 and 500 CO2 Equivalent Tonnes. The new requirements have taken effect from 1st January 2015, except for systems with a charge below 3kg (6kg for hermetic systems) where it will apply from 1st January 2017.

I have found it quite tiresome to calculate each item each time based on the refrigerant charge. I wrote a small spread sheet to speed up the process and to give me an idea for maintenance checks etc.
I have included a copy for others to use and hope it helps you as much as me?

http://www.filedropper.com/refrigerantco2book