Water hardness converter

Water hardness is the dissolved calcium and magnesium, and every country measured it differently. A German degree (°dH) is 10 mg of calcium oxide per litre, a French degree (°fH) 10 mg of calcium carbonate per litre, an English or Clark degree (°e) one grain of calcium carbonate per imperial gallon, and the American grain per gallon (gpg) one grain per US gallon; ppm is milligrams of CaCO₃ per litre, and mmol/l is the chemist's unit. In Britain water below 100 mg/l CaCO₃ counts as soft and above 200 mg/l as hard; the US classes water under 60 mg/l as soft and over 180 mg/l as very hard, and dishwasher and detergent instructions expect one of these scales.