Water Hardness Calculator
Calculate total water hardness from calcium and magnesium concentrations, expressed as CaCO₃, and convert between the common hardness units.
- Hardness = 2.497 × Ca + 4.118 × Mg = 2.497 × 60 + 4.118 × 15 = 211.6 mg/L
Hardness Formula
1 °dH = 17.848 mg/L, 1 °fH = 10 mg/L, 1 gpg = 17.118 mg/L CaCO₃
The factors 2.497 and 4.118 are the ratios of the equivalent weight of CaCO₃ (50.04) to those of calcium (20.04) and magnesium (12.15). The classification shown uses the common US scale (soft below 60 mg/L, moderately hard 60 to 120, hard 120 to 180, very hard above 180).
Worked example
Water with 60 mg/L calcium and 15 mg/L magnesium has a total hardness of about 211.6 mg/L as CaCO₃ (11.9 °dH), which is very hard.
Frequently Asked Questions
What is water hardness?
The concentration of calcium and magnesium ions, usually expressed as the equivalent amount of calcium carbonate.
Is ppm the same as mg/L?
For dilute water solutions, yes: 1 mg/L is about 1 ppm by mass.
What is the difference between °dH and °fH?
They are German and French hardness degrees: 1 °dH equals 17.848 mg/L CaCO₃ and 1 °fH equals 10 mg/L.
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