[mulmen]

Venti is not a US Customary Unit.

[Taniwha]

No but it is one used in commerce ....

Customer: Venti? is that twenty in Italian?

SB Barista: yes

C: twenty what?

SBB: fluid ounces

C: can't be that, they use metric in Italy, must be litres or millilitres

SBB: litres

(at least that's what they usually answer when I try it)