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.