I was lucky enough to get a very large supply from a friend's 99 plant grow. I had it tested once and it was very accurate to what I had been measuring the mg. What I did was take an average THC % of 15. Being that it was such a large grow of multiple strains, and giving an estimate that they ranged anywhere from low teens to mid twenties for THC%, I picked 15% for my measurement.
Now, given that 1 gram = 1000 mg. I use 150 mg per 2lbs clarified butter. So that is 150,000 mg. Now multiply that by 15% = 22500mg. That is 22500 per 4 cups of butter. 5625mg per cup. I get 24 cookies to the batch. So divide 5625 by 24 = 234mg each. This measurement is for un hashed trim. I dry ice my trim before I make my butter, so I deduct some mg percentage off to account for that, Giving me a 150mg cookie. Most of my recipes call for 1 cup butter, so that is how I measure it out when I pour it into containers. The dry ice hash gets turned into liquid gold
I hope I didn't just confuse you