"Venti" is of course Italian for 20, let's ignore the fact that Starbucks appear to invalidly trademarked a number, when I find myself stuck with a Starbucks in an American airport I love to ask "that's Italian for twenty, twenty what?" the usual answer is "fluid ounces" .... but "that can't be true, Italy uses the metric system, it must be litres or millilitres ..." usually they choose "litres", it is a big cup
Of course the American fluid ounce is a weird thing, different from the Imperial fluid ounce (which is exactly 1oz of water at 62F)- a strange historical thing due more to British Kings monkeying with the tax system than anything else