The size of the mate depends on how long you want to drink, how strong you like to drink it, and/or how many people you will be drinking the tea with.
The "size" of our mate cups is written on our pages--listed under "model".
What do we refer to when we specify the ounces for each mate?
We refer only to the amount of yerba (in volume--measured in a common, graduated kitchen 'cup' measure) that we would reasonably place in that mate. The mate should be filled a little over 2/3 full of yerba--leaving a slight slope... at the bottom of which is carefully poured the water for each serving.
A 4-oz. mate is about the visual size of a large tangerine or tangelo. A 5-7-oz. mate is more the size of a medium to large apple. Some of our "gigantes" are the size of grapefruits.
We prefer a 4-oz. (approx. 120ml) mate for the two of us; we drink almost a quart (750ml) of water during one "session"... with this "4-oz." mate; pouring approximately 10ml of hot water each serving. Each serving is drunk down by one person, another serving is poured, and it is passed to the next drinker.
A rough guide for how many ounces to have in your mate might be approx. a minimum 3-oz. for the first drinker and one or two ounces for each additional drinker in the group--depending upon strength and duration of drinking preferences.