Convert calcium and magnesium concentrations into total water hardness as CaCO₃, with a classification.
Result
How to use this tool
Type Ca²⁺ in mg/L from a water report.
Type Mg²⁺ in mg/L from the same report.
The headline result is in mg/L as CaCO₃, with the classification.
The metrics also give mmol/L and grains per gallon.
Formula & worked example
Water with 100 mg/L calcium and 20 mg/L magnesium has hardness about 332 mg/L as CaCO₃ — very hard.
Limitations — read this before you rely on it
Covers calcium and magnesium only, the dominant hardness ions. Other divalent ions are ignored.
Frequently asked questions
The amount of dissolved calcium and magnesium, expressed as an equivalent concentration of calcium carbonate (CaCO₃).
It puts calcium and magnesium on one common scale, so waters with different mixes can be compared.
USGS bands: soft below 60, moderately hard 60–120, hard 120–180, and very hard above 180 mg/L as CaCO₃.
It is not generally a health concern, but it causes limescale in kettles and pipes and reduces soap lather.
A US unit for hardness: 1 grain per gallon equals 17.1 mg/L as CaCO₃.