以下详细说明暂以英文提供。
How much caffeine is in what
A standard 240 ml cup of drip coffee carries about 95 mg of caffeine, a single espresso shot 63 mg, and black tea around 47 mg. Energy drinks land near 80 mg per 250 ml can, cola near 34 mg per 355 ml, and a cup of matcha around 70 mg — gentler than coffee because the leaf is steeped rather than brewed hard. Real-world drinks vary: a large café coffee or a strong cold brew can hold two or three "cups" worth in one go.
Limits and the half-life clock
The FDA points healthy adults at no more than 400 mg a day, teenagers at about 100 mg, and pregnancy guidance usually settles near 200 mg. Caffeine leaves the body on a roughly 5.7-hour half-life: enter the hours since your last drink and the calculator shows what remains — half after one half-life, a quarter after about eleven and a half. That lingering quarter is why a 4 p.m. espresso can still be nudging your sleep at midnight.
中国本地参考
日常计算时值得知道的中国本地规则：
- 计量的单位习惯: 住房面积用平方米，土地常用亩（1 亩 ≈ 666.7 平方米）；里程用公里，油耗用 L/100km。
- 日期与数字格式: 日期写作 2026年10月13日（年-月-日）；大数习惯用万、亿（1 万 = 10,000，1 亿 = 100,000,000）。
- 法定节假日: 全年法定节假日 11 天，春节与国庆为长假；调休安排每年由国务院办公厅发布。
- 速度与限速: 高速公路最高限速 120 km/h，城市快速路多为 80 km/h，均以公里每小时计。
- 鞋服尺码: 鞋码用中国码（毫米制），服装常用 155/80A 这类身高围度组合，与欧美码不同。
数据核对：2026 年 10 月
常见问题
How long until caffeine wears off completely?
Never fully zero, but the effect fades fast in relative terms: about half is gone in 5–6 hours for most adults, and under 10% remains after a full day. Genetics, smoking, medications, and liver health shift the half-life between people.
Is 400 mg safe for everyone?
No — it is the figure for healthy adults. Pregnant people are usually advised toward 200 mg, teens toward 100 mg, and anyone with heart arrhythmia, anxiety disorders, or certain medications should set a personal limit with their doctor.
Does espresso have more caffeine than coffee?
Per ounce, dramatically — but a serving is one small shot at 63 mg versus a full cup of drip at about 95 mg. The small cup is why espresso drinks often end up gentler than a big mug of filter coffee.