Latte ratio: espresso to milk by cup size

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A latte is about one part espresso to four or more parts steamed milk under a thin layer of foam. Breville's guide puts it as 1 part espresso, 4 parts milk (or more) and 1 part foam, and La Marzocco's home guide defines the American latte as an 8 to 12 oz drink built on a double shot with about 8 oz of milk. In cup terms: a double shot (about 2 oz) plus 6 oz of milk fills an 8 oz cup at 1:3, the same double plus 10 oz fills a 12 oz cup at 1:5, and past 12 oz you either add a third shot or accept a milkier drink.

Latte ratio by cup size

The shot volumes come from two published standards. illy's coffee bar manual specifies 7 g of coffee to 25 ml for a single and 50 ml for a double, pulled in 25 to 30 seconds at 9 bar. La Marzocco's beginner's guide uses a modern double of 18 g in and 28 to 36 g out in 25 to 30 seconds. Both land a double between 1.7 and 2 oz, which is why the table says "about 2 oz." The milk figures and ratios in the table are arithmetic from those shot sizes and the cup, not a manufacturer spec.

Why the ratio, not the shot count, sets the flavor

Most shops build a latte on a double shot and keep it there as the cup grows. Breville's latte guide says most coffee shops use two shots for a typical latte, and La Marzocco's recipe is a double shot with 8 oz of milk. Hold the shot constant and every step up in cup size dilutes it. That is the whole reason a 16 oz latte tastes weak next to a 12 oz from the same bar: the coffee did not change, the ratio went from 1:5 to 1:7. If you like the 12 oz and want the 16 oz to taste the same, ask for a third shot rather than a darker roast.

The same logic explains the neighbors on the menu. La Marzocco's guide gives the cortado as a double shot with 2 oz of milk (1:1), the modern cappuccino as a double with 4 oz of milk in a 6 oz cup, and the flat white as a double with about 4 oz of milk and a thinner foam layer. A latte is the only one of the four where milk outweighs espresso by four or more to one. Our cortado vs latte and flat white vs cappuccino pages go through those side by side.

Milk temperature and foam depth

Breville and La Marzocco agree on the milk: steam to 140 to 150 F. La Marzocco puts the microfoam layer at about 1 cm; Breville describes it as a thin layer. Foam counts toward the milk volume in the table above, so a latte with a thick cappuccino cap is a different drink even at the same ratio. Whole milk is the standard for texture; Breville's guide notes baristas generally agree it froths best and names oat milk as the plant-based choice that steams well. Whatever milk you use, keep the ratio the same and judge by taste; the ratio is the variable that moves flavor most.

Making the numbers at home

Pull a double into the cup, weigh it if you can (aim for 28 to 36 g out from 18 g in, per La Marzocco), then steam milk by cup size: 6 oz for an 8 oz cup, 8 oz for a 10 oz cup, 10 oz for a 12 oz cup. Steam a little more than you need, since some stays in the pitcher. Breville's caffeine note for scale: a 12 oz latte with two shots runs around 125 mg by their estimate. A pitcher marked in ounces makes the ratio repeatable: milk frothing pitchers on Amazon. The full method, including how to steam without a machine, is in how to make a latte.

Sources

Breville: Macchiato vs latte (1 part espresso, 4 parts milk, 1 part foam)
Breville: How to make a latte
La Marzocco Home: The beginner's guide to espresso drinks
illy: Coffee Bar Manual, espresso preparation (PDF)