How it is calculated
The factors turn the elements into a calcium-carbonate equivalent. If the lab report already states the hardness, this screen is not needed.
mg/L CaCO₃ = 2,497 × Ca + 4,118 × Mg
Where the numbers come from
- Calcium — unit in the field: mg/L
- Magnesium — unit in the field: mg/L
Example
40 mg/L of calcium and 10 mg/L of magnesium give about 141 mg/L as CaCO₃.
Questions
A German degree?
It is about 17,848 mg/L CaCO₃. The second line divides by that number.
Is the calcium in the test already as CaCO₃?
Then do not multiply it again. The field should hold the item itself.
How soft is soft water?
The cutoffs differ from scale to scale. Below 4 °dH is often called soft, but that is a convention, not a diagnosis.