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Water hardness calculator

Their are two types of water hardness. Temporary and permanent hardness. This calculator determines the permanent total hardness. For information about the temporary water hardness click here.

Total permanent water hardness is calculated with the following formula:


The calcium and magnesium hardness is the concentration of calcium and magnesium ions expressed as equivalent of calcium carbonate. The molar mass of CaCO3, Ca2+ and Mg2+ are respectively 100,1 g/mol, 40,1 g/mol and 24,3 g/mol.
The ratio of the molar masses are:

So total permanent water hardness expressed as equivalent of CaCO3 can be calculated with the following formula:

The following calculator computes and gives an indication of the total water hardness. Fields with * are required.

Water Hardness mg/L or ppm of CaCO3
French degree
German degree
English degree


The following values are used to give an indication about the water hardness:

Concentration as CaCO3 Indication
0 to 60 mg/L Soft water
60 to 120 mg/L Moderately hard water
120 to 180 mg/L Hard water
>180 mg/L Very hard water

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Warning: Lenntech BV cannot be held responsible for errors in the calculation, the program itself or the explanation. For questions or remarks please contact us.

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