About a third of a cup of coffee
USDA measures brewed green tea at 12 mg of caffeine per 100 g, which works out to about 29 mg in an 8 fl oz cup. That is roughly a third of an 8 oz cup of drip coffee at USDA’s reference strength (95 mg), and a little over half an 8 oz cup of brewed black tea (47 mg). The FDA’s table of typical drinks, which uses 12 oz servings, lists green tea at 37 mg and black tea at 71 mg.
As with any tea, the figure moves with how much leaf goes into the cup and how long it steeps. Bottled green tea is usually weaker. USDA’s figure for unsweetened bottled green tea matches brewed at 12 mg per 100 g, but its sweetened and diet bottled versions come in at 5 and 4 mg.
Matcha and coffee-shop green tea
Matcha is the exception: the powdered leaf is whisked into the drink rather than steeped and removed. A Grande Starbucks Matcha Latte carries 65 mg, a little over two cups of brewed green tea.
Starbucks’ own brewed green tea, Emperor’s Clouds & Mist, is lighter than home-brewed at small sizes: Starbucks lists 1 to 15 mg for a Short or Tall and 16 to 25 mg for a Grande or Venti. Its Iced Green Tea runs 25 to 30 mg in a Grande.
Where green tea fits
At 29 mg a cup, green tea is one of the easier ways to keep some caffeine in a day without much of it. Thirteen cups stay under the 400 mg daily figure the FDA cites for healthy adults, and six cups stay under the 200 mg daily ceiling ACOG uses in pregnancy.
It is not caffeine-free, though. With caffeine’s mean half-life of about five hours (NCBI), an evening cup still counts. For a cup with no caffeine at all, USDA records zero in brewed herbal and chamomile teas.