Many people wonder how much caffeine tea has relative to coffee. People also wonder whether green tea has more or less caffeine than black tea. The reason there is so much confusion is that caffeine content varies a lot for both tea and coffee. These variations exist due to many factors, including steeping times and the particular kind of beverage involved.
We here at Tozy Tea went to the Mayo Clinic to find the data behind the chart below. It shows the high and low ranges of caffeine content for coffee, green tea and black tea. Even the lowest caffeine coffee has higher caffeine content than the highest caffeine content tea.
According to research by Oba and Nigata, on average green tea will have slightly lower caffeine content than black tea. Green tea, however, has a narrower range, so it is possible for a particular cup of green tea to have a lower or higher caffeine content than a particular cup of black tea. So if you want to cut caffeine intake, choose green tea, but don't be terribly surprised if you get more caffeine than you thought you would.
If you are really worried about caffeine intake, your best bet is a rooibos (aka red tea) blend like Brahms Lullaby or an herbal blend like Northland Blueberry. Both kinds naturally have no caffeine. An herbal or rooibos blend (sometimes called a "tisane") will not have caffeine unless black or green tea is included in the blend. In addition, artificially decaffeinated green or black tea will have only a minimal amount of caffeine.