Matches the iced black tea exactly
Starbucks’ Iced Green Tea carries 20 to 25 mg in a Tall, 25 to 30 mg in a Grande, 40 to 45 mg in a Venti, and 55 to 60 mg in a Trenta, the identical range published for its Iced Black Tea at every size. Both are brewed and served over ice at a similar strength, so the leaf type doesn’t change the dose much here, even though home-brewed green tea generally runs lower than black tea (about 29 mg against 47 mg per 8 oz cup by USDA’s figures).
Much lighter than matcha
This steeped-and-strained iced green tea carries far less caffeine than Starbucks’ Iced Matcha Latte (65 mg in a Grande), because matcha is whisked whole-leaf powder rather than brewed and discarded tea leaves, which pulls much more caffeine into the cup.
For anyone choosing between the two mainly on caffeine grounds, it doesn’t matter which one you pick; the choice between iced green and iced black tea at Starbucks comes down entirely to flavour, since neither publishes a lower figure than the other at any of the four sizes.
Where it fits in a day
A Grande, at 25 to 30 mg, is a small dose next to the 200 mg EFSA assessed as a safe single dose for healthy adults. The largest cup, a Trenta, tops out at 60 mg, under a sixth of the 400 mg daily figure the FDA cites for healthy adults. Under the 200 mg daily ceiling ACOG uses in pregnancy, six Grandes at the top of their range (180 mg) would still fit.