Which hardness units can I convert?

ppm or mg per litre as CaCO3, grains per gallon US, German degrees, French degrees, English degrees (Clarke) and mmol per litre.

What counts as hard water?

As a general classification: 0 to 60 ppm is soft, 61 to 120 moderate, 121 to 180 hard, and above 180 very hard water.

Yes. The note under the tool gives the general classification bands, and all conversions are based on mg per litre as CaCO3.

Enter water hardness and convert between ppm, grains per gallon, German degrees and French degrees.

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General classification: 0–60 ppm soft, 61–120 moderate, 121–180 hard, and above 180 very hard water. Conversions are based on mg/L as CaCO3.