Unlike the green tea comparison, this one has a real answer, because fully oxidised is a fixed destination and partially oxidised is a range. Black tea sits at one end of the same continuum oolong moves along, so the question is not "which category is stronger" but "how close to the black tea end is this particular oolong". A heavily roasted Wuyi oolong is closer to black tea than it is to Baozhong.

Side by side

Why black tea is usually sold broken and oolong is not

The grade difference in that table explains most of the practical behaviour. Black tea is frequently processed as CTC — crush, tear, curl — which produces small hard granules designed to extract fast and completely in a few minutes. That is exactly right for a tea bag and exactly wrong for re-steeping, because everything comes out at once. Oolong is almost always sold as whole leaf, frequently rolled into pellets, precisely because it is meant to give up its flavour slowly over many infusions. If you buy bagged oolong you are buying leaf that cannot do what makes oolong worth buying.

This is also why oolong prices look high per gram. A 100 g pouch at gongfu ratio produces roughly 15 to 20 brewing sessions. The same money in black tea produces a similar number of single mugs, but without the session.

Caffeine: black tea is higher, but not by much

About 47 mg against about 38 mg per 8 oz on USDA averages — a gap of roughly 9 mg, or about 20%. That is less than the gap most people assume exists, and it is smaller than the swing you get from steep time alone. Brew a black tea for three minutes and an oolong for five, and the oolong wins. The reputation black tea has for being much stronger comes partly from caffeine and partly from astringency: fully oxidised tea carries more of the theaflavins and thearubigins that produce that drying, brisk finish, and people read that as strength.

Gongfu changes the arithmetic entirely. At 1 g per 15 ml across eight infusions from a 100 ml gaiwan, a session on one oolong portion can deliver well over 100 mg — more than a mug of coffee — even though each individual pour is small and mild. Anyone tracking total intake should count the session, not the cup. The extraction data behind this is on the oolong tea caffeine page.

Theaflavins, astringency and why black tea feels stronger

Fully oxidised tea contains substantially more theaflavins and thearubigins than oolong does, and those compounds produce the brisk, drying sensation on the tongue. That sensation is astringency rather than taste, and it is why black tea reads as strong even when the caffeine difference is only about 20%. Oolong at the light end has almost none of it, which is why those teas get described as soft or round.

Astringency is also the reason black tea and milk go together: milk proteins bind the polyphenols responsible for the drying finish and the cup becomes smoother. Doing the same to a delicate oolong removes nothing you wanted gone and buries the aromatics you paid for.

Price per cup, honestly

Black tea is cheaper per gram almost everywhere, and cheaper per cup by a smaller margin than it looks. A 100 g pouch of mid-tier oolong brewed gongfu yields roughly 15 sessions; 100 g of loose black tea yields roughly 40 mugs. Divide by the cups each actually produces and the gap narrows a lot, though black tea still wins on price. Where oolong wins is flavour range — no black tea covers the distance between Baozhong and Da Hong Pao.

Iced tea and cold brew

Black tea is the better iced tea if you want something bracing and familiar, and it holds up to sugar and lemon in a way oolong does not. Oolong cold-brewed is sweeter and more delicate, and it is excellent with nothing added. Heavily roasted oolong makes poor iced tea — the roast turns thin and flat when extracted cold — so iced oolong means choosing a light tea deliberately rather than using whatever is already in the cupboard.

If you are choosing for an office or a household

Black tea wins on almost every practical axis: cheaper, more widely available, tolerates a shared kettle at whatever temperature it happens to be at, and nobody will complain. Oolong in a shared kitchen tends to get brewed badly by someone else and then blamed. Keep oolong at home and black tea at work, or keep a roasted oolong at work, which is the one style that survives indifferent handling.

Which should you drink?

Black tea if you want a reliable, strong, no-attention cup, particularly with milk or as iced tea. It is also the cheaper and more widely available category, and the one that survives indifferent water and a busy morning.

Oolong if you want to sit with a pot for half an hour and watch the flavour move. It costs more per gram and asks more of you, and it repays both. Oolong is also the better choice if you find black tea too astringent — partial oxidation keeps more of the catechins intact and produces a softer cup at equivalent strength.

Many people land on both: black tea for the first cup of the day, oolong for the afternoon session. There is no rule that says you pick one.

Where the two blur together

Heavily roasted oolongs and lightly processed black teas meet in the middle. A charcoal-roasted Wuyi rock tea delivers the mineral, toasty weight people expect from black tea while still re-steeping eight times, which no black tea does. If you currently drink black tea and want to move toward oolong without giving up body, start there rather than with a delicate high-mountain tea — that is the opposite end and it will taste like nothing to you. The style map is on oolong tea varieties.

For the other comparison, see oolong vs green tea.