Cold, but not weaker than hot
Home-brewed unsweetened black iced tea carries 20 mg of caffeine per 100 g by USDA’s figures, which works out to about 72 mg in a small 12 fl oz glass and 99 mg in a larger 16.5 fl oz glass. Per ounce, that is close to hot black tea (47 mg in an 8 oz cup, about 6 mg an ounce), since iced tea is typically just hot-brewed tea poured over ice or cold-steeped at a similar strength; the temperature doesn’t remove caffeine.
Homemade versus bottled
This figure is for tea brewed at home or in a restaurant from real leaves or bags. Bottled iced tea from the grocery aisle runs weaker per ounce, about 9 mg per 100 g, because it’s often diluted and blended for a milder taste. Starbucks’ Iced Black Tea sits in between, at 25 to 30 mg in a Grande.
Sweet tea, common in the American South, uses the same base and roughly the same caffeine; the sugar changes the taste, not the dose, the same pattern seen across sweetened and unsweetened versions of most caffeinated drinks.
Where it fits in a day
A medium glass, 99 mg, is well under the 200 mg single dose EFSA assessed as safe for healthy adults. Four medium glasses, 396 mg, come right up to the 400 mg daily figure the FDA cites for healthy adults. In pregnancy, where ACOG uses a 200 mg daily ceiling, two medium glasses already use most of the day’s allowance.