The size can be a single, double, or triple, using a proportional amount of ground coffee, roughly 7, 14, and 21 grams; correspondingly sized filter baskets are used. The Italian multiplier term doppio is often used for a double, with solo and triplo being more rarely used for singles and triples. The single shot is the traditional shot size, being the maximum that could easily be pulled on a lever machine, while the double is the standard shot today.
Single baskets are sharply tapered or stepped down in diameter to provide comparable depth to the double baskets and, therefore, comparable resistance to water pressure. Most double baskets are gently tapered (the “Faema model”), while others, such as the La Marzocco, have straight sides. Triple baskets are normally straight-sided.
Portafilters will often come with two spouts, usually closely spaced, and a double-size basket – each spout can optionally dispense into a separate cup, yielding two solo-size (but doppio-brewed) shots, or into a single cup (hence the close spacing). True solo shots are rare, with a single shot in a café generally being half of a doppio shot.
In espresso-based drinks, particularly larger milk-based drinks, a drink with three or four shots of espresso will be called a “triple” or “quad”, respectively.