The ratios of this never cease to amaze me. Ask anyone in the industry the ratios and they say 1 part espresso, 1 part steamed milk, 1 part foamed milk. As them how big an espresso should be and they say 1 fluid ounce.
So..... a cappuccino is therefore supposed to be a 3fl. oz. drink? Rarely do we see them any smaller than 4.5-5oz, and a wet cappuccino - which is what we are all supposed to be making these days - probably has 1 oz of espresso, 3oz of milk, and 1oz of foam. Or maybe a little more foam and a little less milk.
Either way there seems to be a weird perpetuation of this ratio myth and I don't understand why we can't sit down and work out a correct one. Espresso is a precise art - weights, grinds, extraction times and volumes - yet add milk and it all goes out of the window!