I am not a trainer, buy have been trained. With that in mind, I have seen every size cup used imaginable, but the average observed is always 8 oz or 12 oz. You never know what size shots are used - that leaves only my taste to determine if there will be a return to the store. Few stores want to use glass or china cups and I don’t like paper.
Dimmi cups not included, I use only two size cups, a 200 ml (6.75 oz) for cappuccino and 300 ml (10.1 oz) cup for latte. Only one size shot is used for either cup size - that being 14-14.5 gram of coffee with a light tamp and 2 oz of finished coffee in the cup. For cappuccino, If they like the 200 ml cup strong, I use only 1 to 1.5 oz of steamed milk. If they want it normal, I use 2 to 3 oz of milk and foam on top. All the 300 ml latte cups are just filled up with milk and foam over the double shot (2 oz coffee). Never had a complaint., but sometimes it is noticed they add a little extra sugar to calm it down. Just my way!