What is the proper size for cappuccino and latte cups?

It depends on what you like \r\nI like 5-6 ounce cups.

The basic recipe for cappuccino is: 1:1:1 espresso:steamed milk:foamed milk. As you can see, for a 2 oz double shot of espresso you add 2 oz of steamed milk and 2oz of foam, and this fits into a 6oz glass.

For a cup of Latte I usually take 1:4 espresso to steamed milk.