A standard green tea bag brewed in 8 ounces of hot water contains roughly 25 to 40 mg of caffeine. That’s about a third of what you’d get from the same size cup of brewed coffee, which averages 96 mg. But the actual number in your cup depends heavily on how you brew it.
What Typical Brands Deliver
The Mayo Clinic lists brewed green tea at 29 mg of caffeine per 8-ounce cup, while the FDA puts it slightly higher at 37 mg per 12-ounce serving. Twinings reports 30 to 40 mg per cup for its green tea bags. These numbers all land in a fairly tight range, so if you’re drinking a mainstream bagged green tea with normal brewing, expect somewhere around 30 mg per cup as a reasonable baseline.
Tea bags tend to extract caffeine a bit faster than loose leaf tea. The leaves inside most commercial tea bags are broken into small pieces called “fannings” or dust, which have more surface area exposed to water. That means caffeine dissolves more quickly on the first brew compared to whole loose leaves.
How Steeping Time Changes the Number
The biggest variable you control is how long you leave the bag in the water. Research published in the Journal of Chemical Education measured caffeine extraction at boiling temperature across different steeping times and found a dramatic difference between a quick dip and a long steep:
- 1 minute: about 25 mg per 8-ounce cup
- 2 minutes: about 39 mg
- 4 minutes: about 43 mg
- 6 minutes: about 47 mg
Most of the caffeine comes out in the first two minutes. After that, the curve flattens. So a one-minute steep gives you noticeably less caffeine than a three- or four-minute steep, but going from four minutes to eight doesn’t add much more.
Water Temperature Matters Too
Hotter water pulls caffeine out of tea leaves faster. The same study found that tea steeped in lukewarm water (around 120°F/50°C) for six minutes contained about 30 mg of caffeine, while tea steeped at boiling (212°F/100°C) for just one minute already hit 25 mg. At room temperature, even eight minutes of steeping yielded only about 17 mg.
Green tea is typically brewed at a lower temperature than black tea, around 175°F rather than a full boil. Data from the Sugimoto Tea Company illustrates the gap clearly: a Japanese green tea brewed at 212°F for three minutes delivered 117 mg of caffeine per serving, while the same tea brewed at the recommended 175°F for 45 seconds delivered 68 mg. That’s a 42% reduction just from adjusting temperature and time. For bagged green tea with less leaf, the absolute numbers are lower, but the proportional effect is similar. If you want less caffeine, use cooler water and steep briefly.
Green Tea vs. Coffee and Other Drinks
At around 30 mg per cup, green tea sits on the low end of the caffeine spectrum for hot beverages. An 8-ounce cup of brewed coffee delivers roughly 96 mg, more than three times as much. Black tea falls in the middle at about 47 mg per cup. A 12-ounce can of cola contains around 34 mg, putting it in the same neighborhood as green tea.
The FDA considers up to 400 mg of caffeine per day safe for most adults. At 30 mg per cup, that’s roughly 13 cups of green tea before you’d hit that ceiling. In practical terms, caffeine from green tea is unlikely to be a concern for most people unless you’re drinking it in very large quantities or you’re particularly sensitive to stimulants.
Why Green Tea Feels Different Than Coffee
Many people report that green tea gives them a smoother, more sustained alertness compared to coffee, even accounting for the lower caffeine dose. The reason is an amino acid called L-theanine, which is naturally present in tea leaves. L-theanine promotes relaxation without drowsiness by boosting calming brain chemicals like GABA, serotonin, and dopamine. It also increases alpha brain wave activity, the type associated with a calm, focused mental state.
When paired with caffeine, L-theanine takes the edge off. You still get the alertness and focus, but with less of the jitteriness or crash that a comparable dose of caffeine from coffee might produce. This is one reason green tea is often recommended as a gentler alternative for people who find coffee too stimulating.
Decaf Green Tea Isn’t Caffeine-Free
If you’re choosing decaffeinated green tea bags to avoid caffeine entirely, know that “decaf” doesn’t mean zero. Most decaf teas retain about 1 to 2 percent of their original caffeine content, which translates to roughly 1 to 2 mg per cup. For most people that’s negligible, but if you’re extremely caffeine-sensitive or avoiding it for medical reasons, it’s worth knowing the distinction. Enforcement of decaf labeling is also inconsistent, so some products may contain more than expected.