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Water Hardness from Ca²⁺ and Mg²⁺ Calculator

Hardness as CaCO₃ = 2.5 · [Ca²⁺] + 4.1 · [Mg²⁺] (mg/L).

Compute total water hardness expressed as mg/L of CaCO₃ from calcium (mg/L) and magnesium (mg/L) measurements: Hardness = 2.497 · [Ca] + 4.118 · [Mg]. Also reports the equivalent grains per US gallon (÷ 17.118).

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

mg/L
mg/L

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Hardness (mg/L CaCO₃) = 2.497 · [Ca²⁺] + 4.118 · [Mg²⁺]

In depth

Compute total water hardness expressed as mg/L of CaCO₃ from calcium (mg/L) and magnesium (mg/L) measurements: Hardness = 2.497 · [Ca] + 4.118 · [Mg]. Also reports the equivalent grains per US gallon (÷ 17.118).