Its really not too bad depending on what you are making . I use size 1 caps and every batch i pull out of the capper range from .380 to .420 grams (total filled cap weight) . So if you take into account the ratio between your filler and active ingredient, your total active ingredient is only going to swing a few mg's in either direction depending on what your making .
I cap my aromasin in 10mg caps just because i like working with easy round numbers , but i figure if the total fill weight has a 40mg varience the aromasin in each cap is roughly 8-12mg in a given cap . Not to big a deal with aromasin , but i wouldn't try to cap adex or letrozole because that few milligram swing could fuck you up pretty bad if you are taking what you thought was 1mg and is actually 2 or 3 mgs .