A standard 8-ounce cup of brewed green tea contains about 29 milligrams of caffeine, according to Mayo Clinic data. That’s roughly a third of what you’d get from the same size cup of brewed coffee, which averages 96 milligrams. But 29 mg is just a midpoint. The actual amount in your cup can range from as low as 10 mg to nearly 50 mg depending on the variety, how you brew it, and what form the tea comes in.
How Brewing Changes the Number
The two biggest variables you control are water temperature and steeping time, and both have a dramatic effect on how much caffeine ends up in your cup. Research published through the American Chemical Society measured caffeine extraction at three temperatures and found stark differences. At room temperature (about 68°F), tea steeped for four minutes released only 10 mg of caffeine per 8-ounce cup. At 122°F, that jumped to 24 mg. At a full boil (212°F), the same four minutes produced about 43 mg.
Steeping longer also increases caffeine, but the effect plateaus. At boiling temperature, caffeine peaked around 47 mg at six minutes and didn’t climb further at eight minutes. At lower temperatures, caffeine kept rising steadily through the full eight minutes but never reached the levels that hotter water produced in just one or two minutes. The practical takeaway: if you want less caffeine, use cooler water and steep for a shorter time. If you want a stronger kick, use near-boiling water and let it sit for five to six minutes.
Caffeine by Green Tea Variety
Not all green teas are created equal. The plant’s growing conditions, how much sunlight the leaves received, and the processing method all shift the caffeine content significantly. Here’s how popular Japanese green tea varieties compare per 100 grams of dry leaf:
- Gyokuro: 160 mg, the highest of any common green tea, because the plants are shade-grown for weeks before harvest, which concentrates caffeine in the leaves
- Matcha: 30 mg per 100 grams of powder. Because you consume the entire ground leaf rather than steeping and discarding it, a typical 2-gram serving delivers all of its caffeine directly
- Sencha: 20 mg per 100 grams, the everyday green tea in Japan and the closest to what most people picture when they think of green tea
- Hojicha: 20 mg per 100 grams. The roasting process gives it a toasty flavor but doesn’t significantly reduce caffeine compared to sencha
- Genmaicha: 10 mg per 100 grams, the lowest, partly because the blend includes toasted rice that dilutes the tea leaf content
Tea Bags vs. Loose Leaf
Commercial tea bags often contain finely ground leaf particles rather than whole leaves. These smaller pieces have more surface area exposed to water, which means caffeine extracts faster and more completely on the first brew. If you’re using bagged green tea from the grocery store, your cup may contain somewhat more caffeine than you’d get from loose-leaf tea steeped under the same conditions. The difference isn’t enormous, but it’s worth knowing if you’re trying to keep your intake on the lower end.
Green Tea vs. Coffee and Other Drinks
Green tea sits on the low end of the caffeine spectrum for brewed beverages. An 8-ounce cup of brewed coffee delivers about 96 mg of caffeine, more than three times the amount in green tea. Black tea typically falls somewhere in between. For context, the FDA considers up to 400 mg of caffeine per day a safe amount for most healthy adults. You could drink roughly 13 cups of green tea before hitting that ceiling, compared to about four cups of coffee.
If you want to cut caffeine almost entirely, decaffeinated green tea still contains a trace amount, typically around 2 mg per cup. That’s low enough to be negligible for most people but not technically zero.
Why Green Tea Caffeine Feels Different
Many people report that green tea gives them alertness without the jitteriness or crash they experience from coffee. This isn’t just perception. Green tea contains an amino acid called L-theanine that works alongside caffeine in the body. L-theanine promotes a calm, focused state, and when paired with caffeine, it tends to smooth out the stimulant’s sharper edges. The typical ratio used in research on this combination is two parts L-theanine to one part caffeine, and green tea naturally delivers something close to that balance. The result is a gentler, more sustained lift in attention rather than the spike-and-crash pattern that higher-caffeine drinks can produce. This makes green tea a practical choice for people who are sensitive to caffeine but still want a mild boost.