For anyone unfamiliar with the terminology, while the definition of these can vary depending on where you are it is generally accepted that a lungo is a ‘stretched’ version of an espresso with twice the water. This is not to be confused with any coffee such as an Americano where water is added afterwards, however! All of the water in an espresso lungo is brewed and not added afterwards.
On the other end of the scale, a ristretto is typically a condensed version of an espresso using less water.
There’s no accepted definition of exactly how much makes a ristretto, espresso and a lungo. However, a rough ratio of what they should be like is as follows – 1:1 ristretto, 1:2 espresso and 1:4 lungo. So a lungo would brew approximately double the water of an espresso, and an espresso would brew with about twice the water of a ristretto.