At EVERYMAN I've always coached that a cappuccino is a small 6 ounce espresso drink that is comprised of three equal parts. These three parts should form three distinct layers.
The three layers are as follows:
2. Steamed Milk
3. Frothed Milk
So, what is one to think when you can get a 6oz, 12oz, or even a 21oz Cappuccino? Is the 21oz still equal parts? The NY Times did a piece that helps to unpack what has happened to the classic cappuccino. According to the Times:
"Even among experts, there is considerable disagreement concerning what exactly a cappuccino is".
The article is worth a short read. A few minutes for a lifetime of knowledge.
Post below in the comments what you think makes a good cappuccino? Pictures encouraged!