It's fairly easy... a great way to make about 50caps in about 15 minutes give or take.
Haven't tried the 0 caps which would be needed for that amount, but what I usually do is fill the caps up level them off and measure the difference between a empty cap to get the total.
For most products it comes out fairly close and I just adjust the caps per dose to get the amount I need. For example I cap some tyrosine, the difference is about 500mg to a empty cap so to get 1.5gr per dose I just take 3 at a time.