Strongest per ounce, modest per shot
Espresso is the most concentrated coffee most people drink. USDA measures it at 212 mg of caffeine per 100 g, more than five times the 40 mg per 100 g of drip coffee. But a shot is small. A 1 fl oz single weighs about 30 g, so it carries around 63 mg, less than an 8 oz mug of drip coffee at 95 mg. It takes a double shot, 126 mg, to overtake the mug.
That is why “espresso is stronger” and “espresso has less caffeine” are both true. The first is about concentration, the second about what ends up in the cup.
Shots are the unit coffee shops count in
Most espresso drinks are built from shots, so the shot count, not the cup size, sets the caffeine. Starbucks lists 75 mg for each shot of its signature espresso, a little above USDA’s generic figure, and 85 mg for each blonde espresso shot. A Grande Caffè Latte has two shots (150 mg) and so does a hot Venti; the iced Venti gets a third (225 mg). An Americano adds a shot at every size step, reaching 300 mg in a Venti.
The small, strong drinks follow the same logic. A Starbucks Cortado is three blonde ristretto shots in an 8 oz cup, 230 mg. USDA’s figure for Cuban coffee, sweet espresso served in small cups, is 199 mg per 100 g, close to plain espresso.
Counting it against your day
Four Starbucks shots, a quad, are 300 mg; five are 375 mg, and a sixth takes you past 400 mg, the daily figure the FDA cites for healthy adults. The single-dose view is stricter: EFSA assessed single doses up to 200 mg as not raising safety concerns for healthy adults, and a triple shot (225 mg) already goes beyond that.