A standard 8-ounce glass of brewed black tea contains about 48 mg of caffeine, roughly half what you’d get from a cup of coffee. But that number shifts significantly depending on the type of tea, how hot your water is, and how long you let it steep.
Caffeine by Tea Type
Not all teas are created equal when it comes to caffeine. Here’s what you can expect from an 8-ounce serving brewed under typical home conditions:
- Black tea: about 48 mg
- Oolong tea: about 30 to 55 mg
- Green tea: about 20 to 45 mg, depending on whether the leaves were shade-grown
- White tea: about 15 to 40 mg
- Decaffeinated tea: 1 to 8 mg (caffeine is reduced but never fully removed)
- Bottled tea (ready-to-drink): about 26 mg
Herbal teas made from ingredients like chamomile, peppermint, or rooibos contain no caffeine at all, because they aren’t made from actual tea leaves. If you’re trying to avoid caffeine entirely, those are your safest bet. Decaf tea still carries a small residual amount.
How Brewing Changes the Number
Water temperature and steeping time are the two biggest levers you control. Research published by the American Chemical Society tracked caffeine extraction from black tea at three different temperatures and found dramatic differences. At room temperature (about 68°F), an 8-minute steep pulled only around 17 mg of caffeine into the cup. At 122°F, that same steep time yielded roughly 37 mg. At a full boil (212°F), caffeine reached about 47 mg in just six minutes.
The pattern is straightforward: hotter water extracts caffeine faster. At boiling temperature, most of the caffeine releases within the first four to six minutes, then plateaus. Steeping longer than that doesn’t add much more. At lower temperatures, caffeine keeps climbing slowly through eight minutes and beyond, but never catches up to a hot brew.
To put that in practical terms: if you steep black tea in boiling water for just one minute, you’ll get around 25 mg of caffeine. Double the time to two minutes and you’re near 39 mg. By four minutes, you’re at roughly 43 mg. After six minutes, the cup is essentially maxed out. So a quick dunk gives you about half the caffeine of a full steep.
Tea Bags vs. Loose Leaf
Tea bags generally deliver more caffeine per cup than loose leaf tea, and the reason is particle size. The tea inside most bags is cut into very small pieces (sometimes called “fannings” or “dust”), which exposes more surface area to the water. That means caffeine and other compounds extract faster and more completely. Whole loose leaves release their caffeine more gradually, so a typical loose leaf cup brewed for the same amount of time tends to come in a bit lower. The difference isn’t enormous, but it’s consistent enough to notice if you’re paying attention to your intake.
Tea vs. Coffee and Other Drinks
The average 8-ounce cup of brewed coffee contains roughly 95 mg of caffeine, about double a cup of black tea. A 12-ounce can of cola has around 35 mg. An 8-ounce energy drink typically falls between 70 and 100 mg, though some brands pack much more.
Tea sits in a moderate zone. You’d need to drink about eight cups of black tea to hit the FDA’s general guideline of 400 mg per day for healthy adults. For context, that same limit is only about four cups of coffee. If you’re switching from coffee to tea to cut back on caffeine, you’re roughly halving your intake cup for cup.
What Affects Caffeine Beyond Brewing
The tea plant itself introduces variation before you ever boil water. Younger leaves and buds contain more caffeine than mature leaves. Tea grown in shade (common with certain Japanese green teas) produces higher caffeine levels because the plant compensates for reduced sunlight by increasing its chemical defenses. The specific cultivar matters too, which is why two black teas from different regions can have noticeably different caffeine levels even when brewed identically.
Serving size is the other factor people overlook. The numbers above are all based on an 8-ounce cup. A large mug holds 12 to 16 ounces, which bumps your caffeine proportionally. A tall glass of iced tea from a restaurant could easily be 16 to 20 ounces, putting you in the 60 to 100 mg range for black tea, closer to a cup of coffee than you might expect.