Between green and black tea
USDA reports oolong tea at 16 mg of caffeine per 100 g, which comes out to about 38 mg in an 8 fl oz cup using the same 237 g reference weight USDA applies to brewed black tea. That lands oolong between the two teas it’s made from the same plant as: brewed green tea carries about 29 mg in a cup, and brewed black tea about 47 mg. Oolong’s oxidation level sits between green (barely oxidized) and black (fully oxidized), and its caffeine happens to fall between them too, though the two aren’t directly caused by each other.
As with any tea, the number on the page is a single reference point, not a fixed law. How much leaf goes into the pot, how long it steeps and whether it’s a light or dark-roasted oolong all move the real figure up or down from USDA’s 38 mg.
Against coffee and kombucha
An 8 oz cup of oolong (38 mg) carries well under half the caffeine of an equivalent cup of drip coffee at USDA’s reference strength (95 mg). It’s also stronger than most kombucha, which is typically brewed from a lighter tea base and fermented, landing kombucha’s usual range below a cup of oolong even though both start from tea leaves.
Fitting oolong into a day
At 38 mg a cup, ten cups of oolong stay under the 400 mg daily figure the FDA cites for healthy adults, and five cups stay under the 200 mg daily ceiling ACOG uses in pregnancy, making it one of the lower-caffeine ways to keep a hot drink in rotation through the day.
It still counts toward an evening total, though. With caffeine’s mean half-life of about five hours (NCBI), an oolong drunk after dinner is still roughly half-active five hours later, small as the dose is. For a genuinely caffeine-free hot drink instead, USDA records zero caffeine in brewed herbal tea.