Question: how much caffeine is in an 8 oz glass of tea?
Answer: Caffeine in Tea Most studies show that black tea has between 40 and 120 mg caffeine per 8-ounce serving. 2﻿ Decaf black tea usually contains about 2 to 10 mg of caffeine. Green tea. usually contains around 25 milligrams of caffeine per 8-ounce serving.