tags: [] - coffee/brewing - coffee/brewing/water aliases: - Water hardness unit conversion - Converting hardness units - dH to ppm conversion

Hardness Conversions¶

Tags: #coffee/brewing #coffee/brewing/water Aliases: Water hardness unit conversion, Converting hardness units, dH to ppm conversion Related: Water in Coffee MOC | Hardness | Hardness Units | Water Standards | KH (Carbonate Hardness) Status: ✅ Complete

Overview¶

Water hardness is expressed in multiple units across different countries and applications, which can cause confusion when comparing water reports, equipment specifications, or coffee water recipes from different sources. The primary units are milligrams per litre as calcium carbonate equivalent (mg/L as CaCO₃, numerically equal to ppm as CaCO₃), German degrees of hardness (°dH), French degrees (°f), and English or Clark degrees (°e). Converting between these units allows accurate comparison of SCA water targets, local water reports, and coffee equipment manufacturer specifications.

Hardness Unit Conversion Table¶

From	To mg/L CaCO₃	To °dH	To °f	To °e
1 mg/L as CaCO₃	1.00	0.056	0.10	0.070
1 °dH (German)	17.85	1.00	1.78	1.25
1 °f (French)	10.00	0.56	1.00	0.70
1 °e (English/Clark)	14.3	0.80	1.43	1.00

Quick Reference Conversions¶

mg/L as CaCO₃ to °dH: divide by 17.85 °dH to mg/L as CaCO₃: multiply by 17.85 mg/L as CaCO₃ to °f: divide by 10 °f to mg/L as CaCO₃: multiply by 10

SCA Water Targets in Multiple Units¶

Parameter	mg/L as CaCO₃	°dH	°f	°e
Total hardness (target)	68	3.8	6.8	4.8
Total hardness (min)	17	1.0	1.7	1.2
Total hardness (max)	85	4.8	8.5	5.9
Alkalinity (KH target)	40	2.2	4.0	2.8

Ion-Specific Conversions¶

Hardness from individual ions is calculated by converting ion concentration (mg/L) to CaCO₃ equivalent:

Calcium (Ca²⁺): mg/L Ca²⁺ × 2.497 = mg/L as CaCO₃
Magnesium (Mg²⁺): mg/L Mg²⁺ × 4.118 = mg/L as CaCO₃

Total hardness = Ca²⁺ (as CaCO₃) + Mg²⁺ (as CaCO₃)

Practical Notes¶

European water reports (German, French, Austrian) typically use °dH or °f; multiply by 17.85 or 10 respectively to obtain the SCA-standard mg/L as CaCO₃
UK water reports may use °e (Clark degrees); multiply by 14.3 for mg/L as CaCO₃
Aquarium test kits (used for KH measurement) typically express results in °KH = °dH for carbonate hardness specifically; multiply by 17.85 for mg/L as CaCO₃
Australian water reports generally use mg/L; values are already in the CaCO₃ equivalent format for direct comparison with SCA targets

Key Facts¶

Four main hardness units: mg/L as CaCO₃ (= ppm), °dH (German), °f (French), °e (English/Clark)
1°dH = 17.85 mg/L as CaCO₃; 1°f = 10 mg/L as CaCO₃; 1°e = 14.3 mg/L as CaCO₃
SCA total hardness target: 68 mg/L as CaCO₃ = 3.8°dH = 6.8°f
SCA alkalinity target: 40 mg/L as CaCO₃ = 2.2°dH = 4.0°f
Aquarium KH kits read in °KH ≡ °dH; multiply by 17.85 to convert to SCA unit

References¶

Changelog¶

Date	Change
2026-04-28	Note created

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