What is the definition of a cup of coffee
The most common global standard for recipe and marketing purposes** is 150 ml (5 oz), with a caffeine content around 100 mg. This commonly refers to instant, filter, or drip coffee, or a mixed espresso coffee like a latte

Coffee is traditionally served in a smaller cup than other hot beverages, mainly due to strength and expense. For example, an Italian espresso cup is around 30 to 60 ml (1 to 2 oz) in size, with a caffeine content a little more then 100 mg

Some references


http://www.ico.org/caffeine.asp
http://www.scaa.org/?page=resources&amp;d=cupping-standards


** e.g. marketing description of a "6 cup coffee maker" refers to 6 x 150 ml cups