Tea Caffeine Calculator
Estimate how much caffeine is in your tea and compare your daily intake to safety guidelines. Enter your tea type, steep time, and cup size to personalize the result.
Wondering how much caffeine in tea you are actually drinking? A standard 8 oz (240 ml) cup of black tea typically contains 40–70 mg of caffeine, green tea about 25–45 mg, oolong around 30–50 mg, white tea 15–30 mg, and matcha 60–80 mg per teaspoon whisked into hot water. This calculator multiplies a per-ounce baseline for your tea type by your serving size, scales it for steep time, and totals across the cups you drink in a day so you can see exactly where you land.
For context, the FDA considers up to 400 mg of caffeine per day safe for most healthy adults, while pregnant people are advised to stay under 200 mg. As a quick example, four 12 oz mugs of black tea steeped for 5 minutes can easily push past 300 mg, while three 8 oz cups of green tea steeped 2 minutes usually stay under 120 mg. The tool flags your status (low, moderate, high, or over the limit) and breaks the math down by cup so you can adjust steep time, cup size, or tea type with confidence.
How it works: Pick your tea type, steep time, cup size and unit, and the number of cups per day. The calculator converts your cup size to milliliters, applies a per-ml caffeine rate based on tea type and steep time, multiplies by daily cups, and compares the total to FDA guidelines.
This tool provides educational estimates, not medical advice. If you have a heart condition, anxiety disorder, are pregnant, or take medication, consult a healthcare provider about your personal caffeine limit.
Understanding Caffeine in Tea: What Drives the Number
Caffeine content in tea is not a fixed number on the box — it shifts based on the leaf, how long you steep, how much water you use, and how often you sip. Here is how to read your result and adjust it.
Typical caffeine per 8 oz (240 ml) cup by tea type
| Tea type | Steeped 2 min | Steeped 4 min | Steeped 6+ min |
|---|---|---|---|
| Black tea | 30–40 mg | 45–60 mg | 55–75 mg |
| Green tea | 18–25 mg | 28–38 mg | 35–45 mg |
| Oolong tea | 22–30 mg | 35–45 mg | 45–55 mg |
| White tea | 12–18 mg | 20–28 mg | 25–32 mg |
| Matcha (1 tsp whisked) | 60–70 mg | 60–70 mg | 60–70 mg |
| Pu-erh tea | 30–40 mg | 45–55 mg | 55–70 mg |
| Yerba mate | 55–75 mg | 70–85 mg | 80–95 mg |
| Herbal (chamomile, rooibos) | 0 mg | 0 mg | 0 mg |
Daily caffeine guidelines by life stage (2026)
| Group | Recommended daily ceiling | Roughly equals (black tea, 8 oz, 4 min) |
|---|---|---|
| Healthy adult | 400 mg | About 7–8 cups |
| Caffeine sensitive | 200 mg | About 3–4 cups |
| Pregnant / breastfeeding | 200 mg | About 3–4 cups |
| Teen (12–18) | 100 mg | About 1–2 cups |
| Child under 12 | Avoid added caffeine | 0 cups recommended |
Why steep time matters more than you think
Caffeine is highly water-soluble, so most of it leaves the leaf within the first 3–5 minutes of steeping. A 1-minute steep typically extracts only 40–55% of available caffeine, while a 5-minute steep gets close to 100%. As a rule of thumb, each extra minute up to 5 adds roughly 10–15% more caffeine. After 5 minutes, the curve flattens but flavor compounds keep extracting, which is why long steeps taste bitter even though caffeine barely increases. If you want a lighter cup, pull the bag at 2 minutes rather than switching teas.
Cup size: the silent multiplier
Caffeine values are almost always quoted per 8 oz (240 ml), but most modern mugs hold 10–16 oz. A 16 oz travel mug of black tea steeped 4 minutes can deliver 90–120 mg of caffeine — nearly double the headline number. A good guideline is to multiply the per-cup estimate by (your cup oz ÷ 8). If you drink three 12 oz mugs instead of three 8 oz cups, you are getting 50% more caffeine without changing anything else. The calculator handles this conversion automatically.
Black vs green vs matcha: why matcha wins
Standard brewed teas leave the leaves behind, but matcha is powdered leaf whisked directly into water — you consume the whole leaf. That is why 1 teaspoon of matcha (about 2 g) delivers 60–80 mg of caffeine regardless of steep time. Black tea is oxidized, which slightly increases caffeine extraction speed, while green tea is unoxidized and brews cooler, releasing less caffeine. A practical rule: matcha ≈ 2x black tea ≈ 3x green tea per equivalent serving.
Timing and sleep: the 5-hour rule
Caffeine has a half-life of about 5 hours in healthy adults, meaning a 60 mg cup at 3 pm still has 30 mg circulating at 8 pm. Sleep researchers commonly suggest stopping caffeine 8–10 hours before bedtime. For a 10 pm bedtime, that means last tea around 12–2 pm. Pregnant people, smokers quitting, and those on certain medications can have half-lives of 8–10 hours, so the cutoff should be even earlier. If you drink tea after 3 pm, expect noticeable effects on sleep onset and deep sleep proportions.
Decaf tea is not caffeine-free
Decaffeinated tea retains roughly 2–5 mg of caffeine per 8 oz cup — about 95% removed, not 100%. Four cups of decaf black tea can still add up to 15–20 mg, which matters for very sensitive drinkers or pregnant people watching every milligram. If true zero caffeine is the goal, choose true herbal infusions like rooibos, chamomile, peppermint, or hibiscus. These contain naturally caffeine-free plants rather than processed tea leaves and will not show up on this calculator (the herbal option returns 0 mg).
How tea caffeine compares to coffee
A standard 8 oz cup of brewed coffee contains 80–100 mg of caffeine — roughly 2x the caffeine of an equivalent cup of black tea and 3–4x green tea. However, an espresso shot (1 oz) only carries 60–65 mg, so a single shot is comparable to one strong black tea. A useful rule of thumb: 1 cup of coffee ≈ 2 cups of black tea ≈ 3 cups of green tea ≈ 1 serving of matcha. This is why switching from coffee to tea typically cuts caffeine intake roughly in half without eliminating the morning ritual.
L-theanine: why tea feels different
Tea naturally contains 10–25 mg of L-theanine per cup, an amino acid that promotes calm alertness and partially offsets caffeine jitters. The caffeine-to-L-theanine ratio in green tea (especially matcha and gyokuro) is around 1:1 to 1:2, producing the characteristic 'smooth' energy. Black tea has a higher caffeine-to-theanine ratio (closer to 3:1), so it feels more stimulating. This is why 100 mg of caffeine from matcha often feels gentler than 100 mg from coffee or black tea, even though the numbers on this calculator are the same.
How This Calculator Works: Methodology & Parameter Explanations
Core formula: caffeine_per_cup_mg = cup_ml × base_rate(tea_type) × steep_factor(steep_time); daily_total_mg = caffeine_per_cup_mg × daily_cups; percent_of_limit = daily_total_mg ÷ limit(life_stage). Unit conversion: cup_ml = (serving_unit = 'ml') ? cup : cup × 29.5735. Steep factor: 0.1 at 0 min, 0.4 + 0.12 × minutes for 1–4 min, and 1.0 at 5+ min.
Parameter explanations
| Input | What it means | Impact on results |
|---|---|---|
| Tea type | Selects a baseline caffeine concentration per ml of brewed tea (or per whisked serving for matcha). Black ≈ 0.20 mg/ml, green ≈ 0.12, oolong ≈ 0.15, white ≈ 0.08, matcha ≈ 0.28, pu-erh ≈ 0.18, yerba mate ≈ 0.30, herbal = 0. | Largest single driver of the result — switching from black to white tea cuts caffeine roughly 60%; switching to matcha or yerba mate roughly doubles it. |
| Steep time | Minutes the leaves stay in contact with hot water. Controls how much caffeine extracts from the leaf into your cup. | Each minute up to 5 adds about 10–15% more caffeine; beyond 5 minutes the curve flattens. A 1-minute steep delivers roughly half the caffeine of a 5-minute steep. |
| Cup size + unit | How much liquid you actually drink per cup, in fluid ounces or milliliters. Internally converted to ml. | Linear effect — doubling cup size doubles caffeine per cup. A 16 oz mug delivers 2x the caffeine of an 8 oz cup at identical steep. |
| Cups per day | Total servings of this tea you drink in a typical day. | Linear scaling on daily total. Going from 2 to 4 cups doubles daily caffeine and your percent of the recommended ceiling. |
| Life stage / sensitivity | Selects which daily caffeine ceiling to compare against (400 mg adult, 200 mg pregnant/sensitive, 100 mg teen). | Does not change caffeine in mg, but reframes whether your intake is 'low', 'moderate', or 'over limit'. The same 250 mg is safe for adults but over the limit for pregnancy. |
Assumptions
Baseline mg-per-ml rates are population averages; actual leaves vary ±25% by cultivar, harvest, and grade.
The steep factor models a typical Western brew (200°F water for black/oolong/pu-erh, 175°F for green/white). Cold brew extracts roughly 30–40% less caffeine at the same time.
Tea types and steep times in the keyword and examples are illustrative defaults; the calculator works for any valid combination of inputs, not a fixed scenario.
Daily limits follow FDA (400 mg adult), ACOG (200 mg pregnancy), and AAP (100 mg teen) guidance current as of 2026.
Decaf and herbal are simplified — herbal returns 0 mg, and decaf is not modeled as a separate option in this version.
Parameter meanings
| Input | What it means | Impact on results |
|---|---|---|
| Tea type | Base caffeine per ml for the chosen leaf or preparation | Largest single lever — can change result by 3–4x between white tea and matcha |
| Steep time | Minutes the leaves contact hot water | Each minute up to 5 adds 10–15% caffeine; flat after 5 min |
| Cup size + unit | Volume per cup, converted to ml internally | Linear — 16 oz cup delivers 2x the caffeine of an 8 oz cup |
| Cups per day | Daily servings of this tea | Linear scaling on daily total and percent-of-limit |
| Life stage / sensitivity | Which mg/day ceiling to compare against | Reclassifies the same intake as safe, moderate, or over limit |
| Time of day | When you drink most of your tea | Does not change mg total but flags sleep-impact risk in insights |