Coffee over ice, brewed a little stronger
Generic iced coffee, the kind sold at delis and coffee shops rather than a specific chain’s recipe, is usually brewed stronger than hot drip coffee so it doesn’t taste watered down once ice melts into it. USDA puts it at 31 mg per 100 g, which comes to about 112 mg for a small 12 fl oz cup, 149 mg for a medium 16 fl oz, and 186 mg for a large 20 fl oz.
Ounce for ounce, that is somewhat stronger than hot drip coffee at USDA’s reference strength (95 mg in 8 oz, about 12 mg an ounce against roughly 9 to 10 mg an ounce for iced), because less water goes in to allow for the ice.
Chain iced coffee runs its own numbers
This generic figure is a useful default, but branded iced coffee varies. Starbucks’ Iced Coffee runs on its own recipe and sizes, and canned or bottled iced coffee drinks from the grocery aisle are weaker still per ounce, typically 28 mg per 100 g. Checking the specific brand’s label is the only way to be sure.
Where it fits in a day
A large iced coffee, 186 mg, sits under the 200 mg single dose EFSA assessed as safe for healthy adults, and two of them, 372 mg, would still leave a little room under the 400 mg daily figure the FDA cites. In pregnancy, where ACOG uses a 200 mg daily ceiling, even a small size uses most of that allowance.