I'd like to take an opportunity to clarify the sizes at Starbucks.
A small is...a tall (12 ounces).
A medium is...a grande (16 ounces).
A large is...a venti (20 ounces hot); venti is Italian for twenty.
(Cold drinks are all slightly larger.)
There is also an eight ounce size, called a "short." (This is what you get when you ask for a children's size. Some stores—particularly rest stops or locations added to an existing business—will deny the sizes existence.) You should be able to order anything as a short, which Washington City Paper confirmed in September:
I went to my nearby Starbucks in Adams Morgan and asked the barista for the smallest cup of coffee I could get.(My sister has ordered shorts for years, but I thought you might want a better source than "my sister.")
I was expecting one of those thimble-sized sample cups.
He wasn’t quite sure what I wanted, so he started showing me all the various cups available — the Tall, the Grande, the Venti, the Ubermassenhaft. (OK, I joke about the last one, but only because Starbucks deserves it for corrupting the language.) Among the cups he showed me was this petite white cone that holds a reasonable eight-ounce pour.
“That’s what I want,” I told the barista. “I’ve never seen those before.”
“We use them for espresso,” he said, noting that I could also use it for coffee.
“Why don’t you include those sizes on the menu?” I asked.
“They’re too small.”
The naming system has outraged consumers for years. This is just the company's way of being cute. (If you order a small, you'll get a tall, if you order a medium, you'll get a grande. So no matter what you say, you'll at least get your drink.)
I once made the mistake of saying "tall" at a coffee shop in my hometown and was berated by the local barista. (So don't do that yourself, dear Old Ones.)
Secret Fast-Food Menus: Truth or Myth?, Washington City Paper