headsets is where i use the -1 rule. usually they take 25 or so balls. i don't like to count so i fill it up and take one out. headsets tend to use a wider range of ball sizes too. hubs and bbs are more consistent in the amount and size of the balls. hubs bbs i can usually remember how many they need. 9 10 or 11 for bbs. hubs and bbs are harder to overfill too.