About

Incorrect coffee-to-water ratios produce either bitter, over-extracted cups or weak, sour brews. The Specialty Coffee Association (SCA) defines the optimal brewing ratio as 1:15 to 1:18 by mass for drip methods, targeting a TDS (Total Dissolved Solids) of 1.15 - 1.35% with 18 - 22% extraction yield. A 1g deviation in dose on a 18g basket shifts extraction by roughly 0.5%, enough to cross the boundary between balanced and astringent. This calculator applies method-specific ratio windows validated against SCA protocols, SCAE brew charts, and competition-level barista standards.

Volumetric measurement introduces error of ±15% due to grind size variation and settling. This tool approximates tablespoon and cup conversions using average whole-bean density (5.3g/tbsp), but a 0.1g resolution scale remains the correct instrument. Note: cold brew ratios use immersion-time compensation and are not directly comparable to percolation methods.

Formulas

The core relationship is a simple linear proportion. Given a desired ratio R (expressed as 1:R), the water mass is computed from coffee dose:

W = C × R

Inversely, given a target water volume:

C = WR

Where C = coffee mass in g, W = water mass in g (water density ≈ 1g/ml at brew temperature), R = ratio factor (e.g., 16 for a 1:16 ratio).

Estimated TDS (Total Dissolved Solids) percentage, assuming a target extraction yield E:

TDS = C × EW × 100%

Where E = extraction yield as a decimal (SCA target: 0.18 - 0.22). Unit conversions use: 1oz = 28.3495g, 1tbsp coffee ≈ 5.3g, 1cup water = 236.588ml.

Reference Data

Brew Method	Ratio (Coffee:Water)	Coffee per 250ml Cup	Water Temp	Brew Time	Grind Size	Notes
Pour Over (V60)	1:15 - 17	15 - 16.7g	92 - 96°C	2.5 - 3.5min	Medium-Fine	Bloom 30s with 2× coffee weight
Chemex	1:15 - 17	15 - 16.7g	92 - 96°C	3.5 - 4.5min	Medium-Coarse	Thicker filter absorbs oils
French Press	1:12 - 15	16.7 - 20.8g	93 - 96°C	4min	Coarse	Full immersion; plunge gently
AeroPress	1:11 - 16	15.6 - 22.7g	80 - 96°C	1 - 2min	Fine - Medium	Inverted method allows longer steep
Espresso	1:1.5 - 2.5	N/A (18g dose → 36g yield)	90 - 96°C	25 - 30s	Very Fine	9bar pressure standard
Ristretto	1:1 - 1.5	N/A (18g dose → 18 - 27g)	90 - 96°C	15 - 20s	Very Fine	Shorter pull; sweeter, more concentrated
Lungo	1:3 - 4	N/A (18g dose → 54 - 72g)	90 - 96°C	35 - 50s	Fine	Higher bitterness risk
Moka Pot	1:7 - 10	25 - 35.7g	~100°C (steam)	3 - 5min	Fine - Medium	Fill basket loosely; do not tamp
Cold Brew (Concentrate)	1:4 - 8	Dilute 1:1 - 1:3 before serving	Room temp / 2 - 5°C	12 - 24hr	Extra Coarse	Lower acidity; 65% less acid than hot brew
Cold Brew (Ready-to-Drink)	1:12 - 15	16.7 - 20.8g	Room temp / 2 - 5°C	12 - 24hr	Extra Coarse	No dilution needed
Drip / Auto Brewer	1:15 - 18	13.9 - 16.7g	92 - 96°C	4 - 6min	Medium	SCA Golden Cup standard
Turkish / Ibrik	1:9 - 12	20.8 - 27.8g	Near boiling	2 - 3min	Extra Fine (powder)	Do not filter; allow grounds to settle
Siphon / Vacuum	1:14 - 16	15.6 - 17.9g	92 - 96°C	1 - 2min	Medium	Full immersion with vacuum draw-down
Percolator	1:15 - 17	14.7 - 16.7g	92 - 100°C	7 - 10min	Coarse	Risk of over-extraction from re-cycling
SCA Golden Cup	1:16.7 (exact)	15g	93°C	4 - 8min	Medium	55g/L ± 10%

Frequently Asked Questions

The SCA Golden Cup standard specifies 55g of coffee per 1L of water, which yields exactly 1:18.18 by mass. However, the commonly cited 1:16.7 accounts for water retained in the grounds (approximately 2× coffee weight). The standard targets a TDS of 1.15 - 1.35% in the final cup, not the slurry.

Finer grinds increase surface area exponentially, accelerating extraction. At the same 1:16 ratio, a fine grind may extract 24% (over-extracted, bitter), while a coarse grind extracts only 14% (under-extracted, sour). The ratio must be tuned in concert with grind size: coarser grinds generally pair with stronger ratios (1:12 - 15), while finer grinds pair with weaker ratios (1:15 - 18).

Espresso uses pressure (9bar) to force water through a dense puck, achieving 18 - 22% extraction in 25 - 30s. The short contact time and high pressure mean less water is needed per gram of coffee. A typical double shot uses 18g coffee to 36g liquid (1:2), producing a TDS of 8 - 12%, roughly 8× the concentration of drip coffee.

A level tablespoon of whole beans averages 5.3g, but ranges from 4.5 - 6.2g depending on bean origin, roast level (dark roasts are less dense), and settling. This represents up to ±16% error. For a 15g dose, that means you could be using 12.6 - 17.4g, shifting your effective ratio from 1:14.4 to 1:19.8. A 0.1g resolution scale costs under $15 and eliminates this variance.

Higher temperature increases extraction rate. At 96°C you may need a slightly weaker ratio (1:17) to avoid over-extraction, while at 85°C a stronger ratio (1:14) compensates for slower extraction kinetics. For cold brew at 4°C, the dramatically reduced extraction rate requires either very high concentration ratios (1:5) or extended time (12 - 24hr).

Scaling is not perfectly linear due to water retention. Each gram of coffee absorbs approximately 2g of water. For a single cup with 15g coffee, you lose 30ml to the bed. For a 10-cup batch with 150g coffee, you lose 300ml. Add this retention volume to your target brew water. Some baristas increase the ratio by 0.5 - 1 point (e.g., 1:16 becomes 1:16.5) for batches over 1L.