The difference between a great cup of coffee and a mediocre one often comes down to a single number: the ratio of coffee to water. Get it right and every other variable — grind, temperature, technique — has something to work with. Get it wrong and no amount of premium beans will save you.
The Golden Cup Standard: 1:18 Ratio
The Specialty Coffee Association (SCA) defines the Golden Cup Standard as 55 grams of coffee per litre of water, with an acceptable range of 45–65g/L. In ratio terms, 55g/L translates to approximately 1:18 — one gram of coffee for every 18 grams of water.
Brew Ratio = Water Weight ÷ Coffee Weight
For a 300ml cup at 1:18:
Coffee = 300 ÷ 18 = 16.7g (round to 17g)
The ratio is always expressed by weight, not volume. A tablespoon of light roast weighs less than a tablespoon of dark roast because of bean density differences. A kitchen scale removes this variable entirely and makes your brews reproducible.
Ratios by Method
Every brew method has a range that works best given its contact time, water flow, and filter type.
| Brew Method | Typical Ratio | Notes |
|---|---|---|
| Espresso (modern) | 1:2 to 1:2.5 | 18g coffee → 36–45g output |
| Espresso (ristretto) | 1:1 to 1:1.5 | More concentrated, sweeter body |
| Moka pot | 1:7 to 1:8 | Pack chamber fully, ratio controlled by hardware |
| AeroPress | 1:6 to 1:12 | Wide range; 1:6 for concentrate, 1:12 standard |
| Pour-over (V60) | 1:15 to 1:16 | 20g coffee → 300–320g water |
| Chemex | 1:16 to 1:18 | Thick filter requires slightly more coffee |
| French press | 1:14 to 1:16 | Full immersion; coarser grind |
| Cold brew | 1:7 to 1:10 | Concentrate at 1:7, ready-to-drink at 1:10 |
| Drip machine | 1:16 to 1:18 | SCA Golden Cup range |
Espresso operates at extreme concentration. A 1:2 ratio means 18 grams of ground coffee yields 36 grams of liquid espresso — a tiny, intense shot that forms the base for lattes, cappuccinos, and flat whites. A 1:2.5 "lungo" pulls slightly more water through the same puck for a longer, slightly milder shot.
Grind Size and Its Relationship to Ratio
Grind size and brew ratio work as a pair. When extraction is off, you often need to adjust one or both.
Extraction Yield (%) = (TDS × Brew Water Weight) ÷ Coffee Dose × 100
The SCA target extraction yield is 18–22%. Under 18% tastes sour and thin (under-extracted). Over 22% tastes bitter and dry (over-extracted).
When your grind is correct but flavour is still off:
- Sour / weak → tighten the ratio (more coffee or less water) or grind finer
- Bitter / astringent → loosen the ratio (less coffee or more water) or grind coarser
- Flat / thin → grind finer before adjusting ratio, to increase surface area
The key principle: adjust grind first to fix extraction quality, then adjust ratio to fix strength. Changing ratio without changing grind shifts strength without necessarily improving extraction.
Water Temperature and Extraction
Water temperature controls extraction rate — hotter water dissolves more compounds more quickly.
| Temperature Range | Effect |
|---|---|
| Below 85°C | Under-extraction; sour, thin |
| 88–91°C | Good for dark roasts, reduces bitterness |
| 91–96°C | SCA recommended; suits most roasts |
| 96–98°C | Light roast; maximizes complex acids |
| 100°C / boiling | Over-extraction risk; bitter |
For cold brew, room-temperature water (20–22°C) extracts slowly over 12–24 hours, producing a low-acid concentrate. The 1:7 to 1:10 ratio compensates for lower extraction efficiency at cold temperatures.
A practical rule: if you're using a pour kettle, letting it sit 30–45 seconds after boiling brings it from 100°C to approximately 94–96°C — ideal for most filter methods.
Scaling: Single Cup to Full Pot
The ratio stays constant regardless of batch size. This is the power of weight-based brewing.
For a V60 at 1:15:
| Batch Size | Coffee | Water |
|---|---|---|
| 1 cup | 15g | 225g |
| 2 cups | 25g | 375g |
| 4 cups | 45g | 675g |
| Full Chemex (6 cup) | 50g | 800g |
Note that pour-over has a practical upper limit. Most V60 users find quality degrades above 40–50g of coffee because maintaining consistent water distribution over a large puck is difficult. For larger batches, a Chemex or batch brewer is more appropriate.
A Moka pot is different — the ratio is largely fixed by the hardware. The basket holds a specific volume of grounds and the bottom chamber holds a specific volume of water. You can influence the ratio slightly by tamping (not recommended) or filling the water chamber to different levels, but mostly you're working within constraints.
Dialing In: When to Adjust Up or Down
Dialing in means finding your personal ideal ratio for a specific coffee, brew method, and taste preference. Start at the method's midpoint and taste critically.
Signals to increase coffee (tighten the ratio):
- Cup tastes watery or thin
- Aroma is present but flavour is weak
- You're adding milk or sugar to compensate for lack of body
Signals to decrease coffee (loosen the ratio):
- Cup is overwhelmingly strong
- Drinking a full cup feels like too much caffeine
- Flavour is present but intensity is uncomfortable
Signals to adjust grind instead of ratio:
- Ratio is already at method midpoint but extraction tastes sour → grind finer
- Ratio is already at method midpoint but cup tastes harsh → grind coarser
A useful dialling-in sequence for any new bean on a V60: start at 1:15, taste, note whether the issue is strength or extraction quality, then make one change and brew again. Two or three iterations typically lands a great cup. Document your final ratio and grind setting — different bags of the same bean can behave slightly differently due to roast date and moisture content.