DKHDKH DKH Degrees of carbonate hardness (dKH or °KH; the K is from the German "Karbonathärte") is a unit of water hardness, specifically for temporary or carbonate hardness. Carbonate hardness is a measure of the concentration of carbonates such as calcium carbonate (CaCO) and magnesium carbonate (MgCO) per volume of water. Specifically, 1 dKH is defined as 17.86 milligrams (mg) of calcium carbonate per litre of water, i.e. 17.86 ppm. Since a mole of calcium carbonate weighs 100.09 grams, 1 dKH is equivalent to 0.17832 mmol per litre. dKH are the same as °fH, degrees of French hardness. DKH