How much caffeine is in oolong tea?

A 6 fl oz cup of oolong tea has 30 to 40 mg of caffeine.

That's about a quarter of a cup of brewed coffee, and 9% of the 400 mg a day the FDA cites for most healthy adults.

Source: Center for Science in the Public Interest · checked 10 Nov 2026

When did you have it?

Had at 3 pm, about 12 mg is still in you at an 11 pm bedtime. That should not affect most people’s sleep.

Ranges: the chart uses the middle of the published range (35 mg for this size).

Bedtime

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Sizes

Size	Volume	Caffeine	mg per fl oz
6 fl oz cup shown above	6 fl oz (177 ml)	30 to 40 mg	5.8
8 fl oz cup	8.1 fl oz (240 ml)	38 mg	4.7

Sources: Center for Science in the Public Interest, USDA FoodData Central · checked 10 Nov 2026

Latest time to drink it

For an 11 pm bedtime, a 6 fl oz cup of oolong tea stays under the 50 mg most people sleep fine with, even late in the evening. The table works it out for other bedtimes and for how sensitive you are: it is the latest time to start one so that the caffeine left stays under the line all night.

Bedtime	Very sensitive under 25 mg	Average under 50 mg	Not very sensitive under 100 mg
9 pm	6:05 pm	Any time	Any time
10 pm	7:05 pm	Any time	Any time
11 pm	8:05 pm	Any time	Any time
Midnight	9:05 pm	Any time	Any time
1 am	10:05 pm	Any time	Any time

For a 6 fl oz cup of oolong tea, average clearance (half-life 5 h), 8 hours of sleep. "Any time" means even one at bedtime stays under the line.

How long it lasts

The caffeine from a 6 fl oz cup of oolong tea peaks in your blood about 75 minutes after you start it, at roughly 30 mg. Half of it is gone in about 5 hours for an average adult; that ranges from roughly 3 to 7 hours, and longer in pregnancy or with some medicines.

Time after	3 hours	6 hours	9 hours	12 hours
Still in you	25 mg	16 mg	11 mg	7.1 mg

So one had at 3 pm leaves about 12 mg at 11 pm. How long caffeine lasts explains the curve.

How it compares

Oolong tea is stronger than 54% of the 38 teas we track, by caffeine per serving.

Per fluid ounce (5.8 mg) it is stronger than 72% of them.

To reach 400 mg in a day you would need about 11 of these.

Less caffeine

Snapple Tea 30 mg, 16 fl oz bottle
Green Tea 28 mg, 8 fl oz cup
Jade Leaf Matcha 16 to 40 mg, 1 serving, powder

More caffeine

Starbucks Earl Grey Tea 40 mg, Grande
Starbucks Royal English Breakfast Tea 40 mg, Grande
Kombucha 41 mg, 12 fl oz bottle

Same caffeine: Honest Tea Mint Green Tea.

FAQ

Is oolong tea high in caffeine?

It is moderate. A 6 fl oz cup of oolong tea has 30 to 40 mg, which is 37% of the 95 mg in an 8 fl oz cup of brewed coffee.

How much caffeine is in 8 fl oz cup of oolong tea?

An 8 fl oz cup of oolong tea has 38 mg of caffeine, 3 mg more than a 6 fl oz cup of oolong tea.

Can I drink oolong tea at night?

For most people, yes: even late in the evening a 6 fl oz cup of oolong tea stays under 50 mg at an 11 pm bedtime.

How long does the caffeine in oolong tea last?

It peaks about 75 minutes after you start it. Of the 30 to 40 mg, about 16 mg is still in you 6 hours later and 7.1 mg after 12 hours, for an average adult with a 5-hour half-life.

Does oolong tea have more caffeine than a cup of coffee?

No. A 6 fl oz cup of oolong tea has 30 to 40 mg; an 8 fl oz cup of coffee has 95 mg.

Method and limits

The caffeine figure comes from Center for Science in the Public Interest and the other sources listed above; recipes, brewing and batches vary, so a real serving can differ. The curves use a standard one-compartment model with an average 5-hour half-life and a sleep-friendly line of 50 mg; your own body may clear caffeine faster or slower. How it works has the details.

These are estimates for information, not medical advice.