Water hardness converter
Water hardness is quoted in at least five different units, all measuring the same calcium carbonate concentration.
ppm as CaCO3
ppm
Grains per US gallon
8.763
- German degrees, dGH
- 8.404
- French degrees
- 15.000
- Clark degrees
- 10.523
- Millimoles per litre
- 1.4987
- Calcium as Ca
- 60.06 ppm
- RO water to blend for the target
- 93.3
- Total calcium carbonate
- 30.00
Show the working
- Hardness = 150
- Water volume = 200
- Target hardness = 80
- Grains per US gallon = 150 / 17.118 = 8.762 71
- German degrees, dGH = 150 / 17.848 = 8.4043
- French degrees = 150 / 10 = 15
- Clark degrees = 150 / 14.254 = 10.5234
- Millimoles per litre = 150 / 100.09 = 1.498 65
- Calcium as Ca = 150 * 0.4004 = 60.06
- dilution_ratio = 150 > 0 ? 80 / 150 : 0 = 0.533 333
- RO water to blend for the target = 150 > 0 ? 200 * (1 - 80/150) : 0 = 93.3333
- Total calcium carbonate = 200 * 150 / 1000 = 30
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- 1 grain per US gallon = 17.118 ppm as CaCO3
- 1 German degree = 17.848 ppm; 1 French degree = 10 ppm; 1 Clark degree = 14.254 ppm
Soft water is under 60 ppm, moderately hard 60 to 120, hard 120 to 180 and very hard above that.
Total hardness includes magnesium as well as calcium, expressed as if it were all calcium carbonate.