A home or diner latte scales with the cup
USDA’s food survey data puts a latte at 36 mg of caffeine per 100 g, which comes 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. Because this figure is a survey average across however lattes are actually made and poured, it scales straight with volume: a bigger cup means proportionally more coffee and more caffeine, the same way a bigger mug of drip coffee does.
That is a different rule from a coffee chain, where a latte is espresso and steamed milk in a fixed shot count. A Grande Starbucks Caffè Latte carries 150 mg regardless of the milk on top, and a Venti hot latte carries exactly the same 150 mg as a Grande, because both get two shots. So a 12 oz Small by USDA’s figures (130 mg) and a 16 oz Grande at a chain (150 mg) are closer than the size difference implies, and a home-poured 20 oz Large (216 mg) can outrun a chain’s biggest hot cup.
Against cappuccino and coffee
A latte and a cappuccino share the same USDA figure, 36 mg per 100 g, since both start from the same shot-to-milk ratio in the survey data; the milk foam changes texture, not caffeine. Both sit below an equivalent cup of drip coffee: an 8 oz cup of coffee at USDA’s reference strength has 95 mg, more than an 8 oz latte (86 mg).
Fitting it into a day
A 12 oz Small latte at 130 mg uses less than a third of the 400 mg daily figure the FDA cites for healthy adults, leaving room for two more without approaching the limit. A 20 oz Large at 216 mg is the one size here that passes the 200 mg EFSA assessed as a safe single dose for healthy adults, so treat that size as a full dose rather than a casual top-up.
Ordered in the afternoon, even a Small latte still carries real caffeine: with a mean half-life of about five hours (NCBI), roughly half of its 130 mg is still active five hours later, which matters if evening sleep is a concern.