The name doppio means ”double” in Italian and refers to a double shot or two espresso shots. In Italy, ordering un caffe will get you a single espresso, and ordering a doppio will get you a double shot. It gets confusing that outside of Italy, a 2 oz shot is becoming the standard serving of espresso. It’s also the case for many cafe-style drinks—for instance, lattes, which now tend to have a double shot as their base. An espresso doppio at Starbucks is slightly smaller than elsewhere at 1.5 oz, but it is still double the size of their solo espresso, which is 0.75 oz.

Source: Home Grounds