Same figure as a latte, foam aside
USDA’s survey data gives cappuccino the identical caffeine density as a latte, 36 mg per 100 g, because both drinks are built from the same ratio of espresso to milk; a cappuccino just uses more of that milk as foam instead of liquid. That works out to 86 mg in an 8 fl oz cup, 130 mg in a 12 fl oz Small, 173 mg in a 16 fl oz Medium and 216 mg in a 20 fl oz Large. The foam changes mouthfeel and how quickly you drink it, not the caffeine underneath.
A coffee-shop cappuccino follows a different rule, because chains size caffeine by shot count rather than cup volume. Starbucks lists a Grande Cappuccino at 150 mg, the same two-shot dose as its Grande Caffè Latte, so the chain version and the 16 oz USDA figure (173 mg) land close together even though the shot-based drink doesn’t grow with size the way the survey figure does.
Against straight espresso
A cappuccino’s caffeine ultimately comes from its espresso shots. A single espresso shot carries 63 mg by USDA’s figure, so an 8 oz cappuccino’s 86 mg is roughly what one strong shot or a shot-and-a-bit contributes once milk is added. A double shot (126 mg) is closer to what a 12 oz Small cappuccino delivers.
How the sizes stack up against a daily limit
A Small at 130 mg leaves more than 270 mg of the 400 mg daily figure the FDA cites for healthy adults. The Large size, 216 mg, is the one that crosses the 200 mg EFSA assessed as a safe single dose for healthy adults, by 16 mg, so a Large is worth counting as a full dose on its own rather than pairing it with much else in the same sitting.
Two Small cappuccinos in a day, 260 mg, still leave room under the FDA figure; add a third and you’re at 390 mg, close enough to the ceiling that anything else caffeinated that day should be small.