About 28 mg per cup
An 8 oz cup of brewed green tea has roughly 28 mg of caffeine — compared with ~95 mg in coffee and ~47 mg in black tea. In practice it ranges from about 20 to 45 mg. Compare it across drinks on the caffeine chart. (Typical averages; your cup depends on the leaf and the brew.)
What changes it
- Steep time and temperature — longer and hotter pulls out more caffeine.
- Type — matcha uses the whole ground leaf, so it's stronger (~70 mg); sencha and gyokuro vary.
- Leaf vs bag — quality loose leaf often has more than a supermarket bag.
Why the energy feels different
Green tea pairs caffeine with L-theanine, an amino acid that takes the edge off. The result is calm, steady alertness rather than a coffee-style spike and crash — which is why it suits people who get jittery on coffee.
Will it affect your sleep?
Less than coffee, but it's still caffeine. A late-afternoon green tea is usually fine; an evening one can quietly shave your deep sleep. If you drink it after lunch, check what's left at bedtime with the half-life calculator.
Put it into practice: count green tea toward your daily caffeine limit — it adds up across a day of cups.