The largest drink size Starbucks offers is a trenta, which holds 30 fluid ounces and is available for most beverages, except hot drinks, specialty iced lattes, and Frappuccinos.

Starbucks hasn't clarified why only certain drinks come in trenta cups. Speculation suggests that beverages with high sugar and caffeine content may not be suitable for this size.

For example, the Iced Gingerbread Latte contains 40 grams of sugar in a venti cup, so you can only imagine the sugar content in a trenta.

While these are rules, it doesn't mean customers can't try asking baristas to make an exception. You can always order two drinks if your desired drink doesn't come in a trenta.