Most brew-ratio charts will tell you 1:15 to 1:17 — one gram of coffee to fifteen-plus grams of water. Follow that in a phin and you’ll get a sad, tea-colored cup. Vietnamese phin coffee runs at about 1 part coffee to 5 parts water, and every classic drink is built on top of that concentrate.
Why so strong?
Three reasons, and they reinforce each other. The drink is small — a traditional glass is around 120 ml, closer to a lungo than a mug of drip. It’s built to be cut — with sweetened condensed milk, with ice, or with both, so the coffee has to arrive concentrated enough to still taste like coffee after dilution. And it’s robusta — bold and bitter by nature, a bean that makes sense as a strong small cup rather than a weak large one.
The ratio per drink
The base ratio shifts with the style, because each drink dilutes the brew differently:
- Cà phê đen (hot black): ~1:5. The reference point. Straight concentrate, sipped slowly.
- Cà phê sữa (hot, condensed milk): ~1:5. Same brew; about a fifth of the cup is condensed milk waiting at the bottom.
- Cà phê sữa đá (iced): ~1:4. Brewed stronger because roughly a third of the glass is ice, and ice melts — the sữa đá guide shows the full build.
- Bạc xỉu: ~1:7 equivalent. The coffee is a seasoning over a glass of milk and ice — see what bạc xỉu is.
The numbers, per cup size
Hot black coffee (cà phê đen) at standard strength, from the calculator’s own math:
| Cup | Coffee | Water | Brew time |
|---|---|---|---|
| 120 ml | 24 g | 155 ml | ~4:40 |
| 180 ml | 36 g | 235 ml | ~6:40 |
| 240 ml | 48 g | 310 ml | ~8:40 |
Two details the table already accounts for, so you don’t have to: the grounds absorb about 1.5 ml of water per gram (that’s why the water column is more than the cup size), and doses above ~25 g need a bigger phin than the standard 4 oz — brew twice instead.
Strength is a preference, not a rule
1:5 is the center of the road. Like it softer, go to 1:6; like it to hum, 1:4.5. The calculator shifts the whole recipe when you move the strength slider, and the brewing guide covers the technique that makes the ratio actually extract — grind, bloom, and a drip you can set a watch to.