Carbonate hardness is usually expressed either in degrees KH (°dKH) (from the German "Karbonathärte"), or in parts per million calcium carbonate ( ppm CaCO3 or grams CaCO3 per litre|mg/L).
One dKH is equal to 17.848 mg/L (ppm) CaCO3, e.g. one dKH corresponds to the carbonate and bicarbonate ions found in a solution of approximately 17.848 milligrams of calcium carbonate(CaCO3) per litre of water (17.848 ppm).
An aqueous solution containing 120 mg NaHCO3 (baking soda) per litre of water will contain 1.4285 mmol/l of bicarbonate, since the molar mass of baking soda is 84.007 g/mol.
Carbonate hardness should not be confused with a similar measure Carbonate Alkalinity which is expressed in either [milli[equivalent]s] per litre (meq/L) or ppm.
In a solution where only CO2 affects the pH, carbonate hardness can be used to calculate the concentration of dissolved CO2 in the solution with the formula CO2 = 3 × KH × 10(7-pH), where KH is degrees of carbonate hardness and CO2 is given in ppm by weight.
[citation needed] The term carbonate hardness is also sometimes used as a synonym for temporary hardness, in which case it refers to that portion of hard water that can be removed by processes such as boiling or lime softening, and then separation of water from the resulting precipitate.