Coffee Brew Ratio Calculator

The single most important variable in coffee brewing

Brew ratio, meaning the relationship between coffee grounds and water, controls strength and extraction more than any other single variable. Get it right and everything else becomes fine-tuning.

The basic formula:

Brew ratio = Water (g) ÷ Coffee (g)

So 300 g of water with 18 g of coffee is a 1:16.67 ratio, which rounds to 1:17.

This works because water and coffee are weighed by gram — making the math universal regardless of measurement system. 1 gram of water = 1 mL = 0.034 fl oz, so the same recipe translates to any measurement system.

The “Golden Ratio” of filter coffee

The Specialty Coffee Association (SCA) defines a “Golden Cup Standard” for filter coffee:

• Brew ratio: 1:18 (55g coffee per 1 liter water)
• Extraction yield: 18-22%
• Total dissolved solids (TDS): 1.15-1.35%
• Brew temperature: 200°F ± 5°F (93°C ± 3°C)
• Total brew time: 4-6 minutes (varies by method)

The Golden Cup is the international quality benchmark. Most specialty coffee shops worldwide target these parameters.

Brew ratios by method

Different brew methods optimize at different ratios:

Why different methods need different ratios

The same beans produce different drinks via different methods because:

1. Contact time: French press 4 min vs espresso 30 sec
2. Pressure: espresso 9 bars vs filter atmospheric
3. Water temperature: lower temps (cold brew) extract less per gram
4. Grind size: espresso fine vs French press coarse
5. Filter type: paper absorbs oils; metal allows oils through

These differences mean equivalent strength requires different coffee amounts.

Strength vs extraction, the two-axis problem

Coffee professionals think in two dimensions:

Strength (TDS): how much coffee solids are dissolved

• Weak: <1% TDS (watery)
• Medium: 1-1.5% TDS (standard filter)
• Strong: 1.5-2% TDS
• Espresso: 8-12% TDS

Extraction yield (%): percentage of coffee mass that ended up in the cup

• Under-extracted: <18% (sour, lacking body)
• Properly extracted: 18-22% (balanced)
• Over-extracted: >22% (bitter, ashy)

The relationship:

TDS = (Coffee × Yield) ÷ Beverage mass

Beverage mass, not brew water. The grounds keep roughly 2 g of water per gram of coffee, so at 1:16 about a tenth of what you poured never reaches the cup. That gap is large enough to matter if you own a refractometer, and irrelevant if you do not.

You can have weak but over-extracted coffee (sour and watery). Or strong but under-extracted (acidic and intense). Or weak and properly extracted (balanced, light). Tuning both ratio and grind size lets you target both axes.

Adjusting strength with ratio

To make coffee stronger or weaker:

Stronger: lower ratio (e.g., 1:14 instead of 1:17)

• More coffee per water
• More body, intensity
• Easy to do but doesn’t change extraction

Weaker: higher ratio (e.g., 1:18 instead of 1:15)

• Less coffee per water
• Lighter body
• The extraction sweet spot shifts a little

By diluting after brewing:

• “Café au lait” style: brew strong, dilute with hot water
• “Cup down” style: brew strong, drink small portions
• Fewer variables, because the extraction itself never changes

Adjusting flavor with grind size

Grind affects extraction independently from ratio:

Finer grind:

• More surface area
• More extraction per second
• Can become over-extracted if too long
• Best for short contact methods (espresso)

Coarser grind:

• Less surface area
• Less extraction per second
• Less risk of over-extraction
• Best for long contact methods (French press, cold brew)

Same ratio with different grinds produces different cups. The interplay between grind and ratio is where coffee gets complicated.

The water side

Water quality dramatically affects coffee:

Minerals (TDS in water):

• 0-50 ppm: distilled, “flat” coffee
• The SCA target is 150 mg/L with an acceptable band of 75-250 mg/L
• 150-300 ppm: harder water, more body
• 300+ ppm: too hard, mineral taste

Specific minerals:

• Calcium and magnesium: enhance extraction
• Bicarbonate: balances acidity
• Sodium: usually neutral

pH: ideal 6.5-7.5 (slightly acidic to neutral)

For best coffee:

• Use filtered water (not distilled, not tap with chlorine)
• Specialty water brands (Third Wave Water, Black Water) for purists
• Brita filter removes chlorine and some minerals

The recipe by brew method (practical guide)

French press for 4 cups (1 liter water):

• Coffee: 67g (1:15 ratio)
• Water at 200°F
• Steep 4 minutes
• Plunge slowly
• Pour immediately to avoid over-extraction

Pour-over for 1 cup (300g water):

• Coffee: 18g (1:16.7 ratio)
• Water at 200°F
• Bloom 30 sec with 40g water
• Pour rest in 3 pulses over 3 minutes
• Total time: 3-4 minutes

Drip machine for full pot (1.5L water):

• Coffee: 85g (1:17.5 ratio)
• Use filtered water reservoir
• Brew runs 6-10 minutes typical

AeroPress standard recipe:

• Coffee: 14g (1:14 ratio with 200g water)
• Water at 175-185°F (lower than other methods)
• Steep 1 minute
• Press 30 seconds
• Total time: 1.5-2 minutes

Cold brew (concentrate):

• Coffee: 100g (1:6 ratio with 600g water)
• Steep 12-24 hours at room temp
• Filter
• Dilute 1:1 with water/milk when serving

Common ratio mistakes

1. Volumetric measurement: scoops and cups vary; weigh by gram
2. Same ratio everywhere: French press needs more coffee than pour-over
3. Ignoring grind size: ratio alone doesn’t control everything
4. Water too cool for the method: below about 195°F most filter brewing under-extracts. AeroPress and cold brew are the deliberate exceptions
5. Boiling water: water at boiling can over-extract
6. Old beans: stale beans extract poorly regardless of ratio
7. Same recipe for all roasts: light roasts need more coffee, water, or time
8. Tap water: chlorine and minerals affect flavor
9. Wrong filter: cheap paper filters absorb oils unevenly
10. No bloom in pour-over: skipping CO2 release ruins extraction

Caffeine considerations

Caffeine per cup varies dramatically:

Stronger ratio = more caffeine per ml. Light and dark roasts hold about the same caffeine by weight, since caffeine survives roasting nearly intact. The difference people notice comes from measuring by scoop: light-roast beans are denser, so a scoop of them weighs more and carries more caffeine.

One closing opinion, since nobody else will say it plainly: most home coffee is too weak. People inherit a scoop from a drip machine manual and never revisit it. If your coffee has always tasted thin and you have been blaming the beans, start at 1:15 and work outward from there.