Weaker than home-brewed, by design
Generic bottled black iced tea averages 9 mg of caffeine per 100 g by USDA’s figures, about 33 mg in a 12 fl oz bottle, 45 mg in a standard 16 fl oz bottle, and 56 mg in a 20 fl oz bottle. That is noticeably weaker per ounce than home-brewed iced tea (about 72 mg for the same 12 oz), because many bottled blends are cut with more water and sweetener to soften the taste.
A generic average, and real brands vary
This is USDA’s broad category average, not any one product. Pure Leaf Unsweetened Black Tea, for example, carries 54 mg in its larger 18.5 fl oz bottle, closer to home-brewed strength than the generic figure suggests. Checking the label is the only way to know a specific bottle’s dose.
Sweetened and unsweetened track similarly
Whether a bottle is sweetened with sugar or sold unsweetened doesn’t change USDA’s category figure much, since the caffeine comes from the tea itself rather than the sweetener. What varies more is how much actual tea versus water and flavouring went into the blend, which is set by each manufacturer’s own recipe and isn’t something the label always spells out clearly.
Where it fits in a day
A 16 oz bottle, 45 mg, is far under the 200 mg single dose EFSA assessed as safe for healthy adults. Eight bottles, 360 mg, would be needed to approach the 400 mg daily figure the FDA cites for healthy adults. In pregnancy, where ACOG uses a 200 mg daily ceiling, four bottles use most of the day’s allowance.