tags: [] - coffee/brewing - coffee/brewing/water aliases: - Water hardness units - Degrees of hardness - ppm hardness CaCO3

Hardness Units¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: Water hardness units, Degrees of hardness, ppm hardness CaCO3 Related: Water in Coffee MOC | Hardness | Hardness Conversions | KH (Carbonate Hardness) | Water Standards Status: ✅ Complete

Overview¶

Water hardness is expressed in multiple units depending on the country and application. The most common units encountered in coffee water management are milligrams per litre as calcium carbonate equivalent (mg/L as CaCO₃), German degrees of hardness (°dH), French degrees (°f), and English degrees (°e or Clark). The Specialty Coffee Association expresses all water quality parameters in mg/L as CaCO₃, which is numerically identical to parts per million (ppm) as CaCO₃ — making this the primary reference unit for coffee water assessment.

Units in Detail¶

mg/L as CaCO₃ (= ppm as CaCO₃)¶

The SCA standard unit. Milligrams of calcium carbonate equivalent per litre of water. Numerically identical to ppm (parts per million) as CaCO₃ because 1 litre of water weighs approximately 1 kg (1000 g = 1,000,000 mg), so 1 mg/L = 1 ppm.

Used in: SCA standards, Australian/New Zealand water reports, US EPA water reports
SCA total hardness target: 68 mg/L as CaCO₃
SCA alkalinity target: 40 mg/L as CaCO₃

°dH (Deutsche Härte — German Degrees of Hardness)¶

The traditional German unit, still widely used in German, Austrian, Swiss, and European equipment specifications.

1°dH = 17.85 mg/L as CaCO₃
Defined as 10 mg CaO (calcium oxide) per litre, equivalent to 17.85 mg CaCO₃ per litre
SCA total hardness target in °dH: 3.8°dH
Very commonly used in European café contexts; dishwasher and espresso machine manuals in Europe frequently specify target hardness in °dH

°f (Degrés Français — French Degrees)¶

Used in France and some other French-speaking countries; also appears in EU water quality documents.

1°f = 10 mg/L as CaCO₃
Conveniently, 1°dH ≈ 1.78°f
SCA total hardness target in °f: 6.8°f

°e or °Clark (English / Clark Degrees)¶

Historical British unit; less common today. Named after chemist Thomas Clark.

1°e = 14.3 mg/L as CaCO₃ (equivalent to 1 grain of CaCO₃ per Imperial gallon)
Still occasionally seen in older UK plumbing documents and water quality reports
SCA total hardness target in °e: 4.8°e

mg/L as Ca²⁺ or Mg²⁺¶

Some water quality reports express calcium and magnesium directly as elemental concentrations: - mg/L Ca²⁺ × 2.497 = mg/L as CaCO₃ - mg/L Mg²⁺ × 4.118 = mg/L as CaCO₃

This requires calculation before comparison with SCA targets — see Hardness Conversions.

Key Facts¶

SCA standard unit: mg/L as CaCO₃ (= ppm as CaCO₃)
1°dH = 17.85 mg/L as CaCO₃; the most common European unit; used in equipment manuals
1°f = 10 mg/L as CaCO₃; used in France and some EU documents
1°e = 14.3 mg/L as CaCO₃; historical British unit, rarely used today
SCA total hardness target: 68 mg/L as CaCO₃ = 3.8°dH = 6.8°f = 4.8°e

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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