What is the correct amount of milk to put into a macchiato? Does it depend on the amount of espresso?
The Italian word macchiato literally means "marked" or "stained" (related to the word "immaculate" ), so really it is an indication to add a small quantity of the "staining" liquid, be it espresso or milk.
A caffe macchiato (also called espresso macchiato) is a shot of espresso (or two) with a "stain" of steamed milk and sometimes a little foam to indicate there is milk hiding under the espresso's crema.
A latte macchiato is the opposite concept, where steamed milk is "stained" by a shot of espresso.
As with any of these drinks, the variations are endless, so recipes and even ratios would be specific to a particular cafe.
This question will largely be based off of the individual tastes of the person consuming the drink.
From my experience as a barista, typically for every ~2 ounces (Double Shot) of espresso, you'll want about 2-3 spoonfuls of milk froth.
Of course, some people enjoy more or less.