Water Hardness Calculator
Calcium and magnesium as CaCO₃, in every unit used.
Work out Water Hardness. Calcium and magnesium as CaCO₃, in every unit used. Written for the problem set you are stuck on.
From a water report, as the element rather than as CaCO₃.
Total hardness as CaCO₃
249.2 mg/L
Very hard · 14.56 grains per gallon
Everything is converted to "as CaCO₃" because that is the convention every water report uses. It lets calcium and magnesium be added together despite their different molar masses — 1 mg/L of calcium counts as 2.50 mg/L of hardness, while 1 mg/L of magnesium counts as 4.12. The usual bands are under 60 mg/L soft, 60–120 moderately hard, 120–180 hard and above 180 very hard. Water softeners are typically sized in grains per gallon, which is why that unit is here too. Hardness is what scales kettles and reduces lather. It is not a health concern at ordinary levels — hard water is a nuisance rather than a hazard, and some studies associate it with mild cardiovascular benefit.
How the Water Hardness Calculator works
Enter the calcium and magnesium from a water report and this converts both to the calcium carbonate equivalent that every hardness scale is built on, then reports the total in mg/L, grains per gallon and German degrees.
Also known as: grains per gallon calculator · ppm to grains hardness converter · how hard is my water · calcium hardness calculator
Frequently asked questions
How is water hardness calculated?
Convert calcium and magnesium to their calcium carbonate equivalents and add them. One mg/L of calcium counts as 2.50 mg/L of hardness and one mg/L of magnesium as 4.12, because of their different molar masses.
What counts as hard water?
Under 60 mg/L as CaCO₃ is soft, 60 to 120 moderately hard, 120 to 180 hard, and above 180 very hard. Most water reports state the figure in these terms already.
What is a grain per gallon?
The unit water softeners are sized in, mostly in the United States. One grain per US gallon is 17.1 mg/L as CaCO₃, so 250 mg/L water is about 14.6 gpg.
Is hard water bad for you?
No, at ordinary levels it is a nuisance rather than a health concern — it scales kettles, reduces lather and marks glassware. Some epidemiological studies associate hard water with a small cardiovascular benefit.
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