Tea Caffeine Calculator
A transparent estimate of the caffeine in your cup, from the tea type, cup size, leaf dose, and steep time — not a lab measurement.
Estimated caffeine
This is a rough estimate, not a measurement. Real cups vary widely by cultivar, leaf grade, and water: measured brewed white, green and black teas have run from 14 to 61 mg a serving, so the range is half to double the estimate (a rule of thumb). Count the top of it. It is not health or medical guidance.
For most adults, the FDA cites 400 mg a day, from all sources combined (coffee, tea, soda, chocolate), as an amount not generally associated with negative effects.
In pregnancy, ACOG describes moderate intake as less than 200 mg a day.
Children and teens should have less; talk with their doctor about caffeine.
Some conditions and medications make people more sensitive to caffeine. If that applies, or you are pregnant, trying to become pregnant or breastfeeding, ask your doctor what limit is right for you.
How the estimate is built
The calculator starts from commonly cited average milligrams of caffeine in a standard 240ml cup for each tea type at a typical leaf dose and steep time, then scales that figure with the actual cup size and leaf amount you enter. Steep time is modeled with diminishing returns — caffeine extracts quickly at first and then more slowly, so a longer steep adds some caffeine but not proportionally more.
Every number here is a starting estimate, not a certified value. If caffeine intake matters to you for a specific reason, this tool is not a substitute for professional or medical guidance.
Frequently Asked Questions
How accurate is this estimate?
It's a rough estimate, not a lab result. Actual caffeine in a cup of tea depends heavily on cultivar, leaf grade, growing conditions, and processing — published figures for the "same" tea type can vary by two or three times. Use this as a ballpark, not a precise figure.
Why does black tea generally have more caffeine than green tea?
It's more about leaf grade and how the leaf is processed than oxidation itself — black tea is often produced from more mature leaf and cut smaller (as in CTC production), which increases surface area and extraction. Young buds and delicate leaf grades, common in green and white tea, tend to yield less caffeine per cup on average, though there's plenty of overlap.
Does steeping longer add a lot more caffeine?
Some, but with diminishing returns. Most caffeine extracts in the first couple of minutes; doubling the steep time does not double the caffeine. This calculator models that with a sub-linear curve rather than a straight multiplication.
Are herbal tisanes really caffeine-free?
True herbal tisanes — chamomile, peppermint, hibiscus, rooibos, and similar — come from plants other than the tea plant (Camellia sinensis) and are naturally caffeine-free, which is what this calculator assumes. A few plant-based drinks sometimes lumped in with "herbal tea," like yerba mate or guayusa, do contain caffeine and aren't covered by this tool.
Estimate only, for general interest — not a medical, health, or nutritional determination. If caffeine affects your health, consult a qualified professional and check a lab-tested source.