How this calculator works
Hardness expresses calcium and magnesium in equivalent calcium-carbonate units. Enter dissolved ion concentrations as elemental Ca and Mg, not their salts. The published water-analysis factors 2.497 and 4.118 convert each contribution. Other multivalent ions can matter in unusual waters; this model uses only the two main contributors. The classification follows USGS bands and is a description of mineral content, not a drinking-water safety determination.
Formula
Hardness(mg/L as CaCO3) = 2.497 Ca(mg/L) + 4.118 Mg(mg/L). One dH is approximately 17.848 mg/L as CaCO3.
Worked example
Calcium at 40 mg/L and magnesium at 10 mg/L gives 99.88 + 41.18 = 141.06 mg/L as CaCO3, classified as hard. At the same hardness and magnesium, the inverse gives 40 mg/L calcium.
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Frequently asked questions
Is calcium carbonate necessarily dissolved in the sample?
The phrase as CaCO3 is a reporting basis, not a claim that all dissolved ions occur as calcium carbonate.
Is hard water unsafe?
Hardness alone does not establish safety. Other chemical and microbial measurements are separate.
Does this measure temporary hardness?
No. Carbonate and non-carbonate hardness require alkalinity and additional water chemistry.