In North America, the hardness of water is often measured in grains per U.S. gallon () of calcium carbonate equivalents. Otherwise, water hardness is measured in the dimensionless unit of parts per million (), numerically equivalent to concentration measured in milligrams per litre. One grain per U.S. gallon is approximately . Soft water contains of calcium carbonate equivalents, while hard water contains .
In North America, the hardness of water is often measured in grains per U.S. gallon () of calcium carbonate equivalents. Otherwise, water hardness is measured in the dimensionless unit of parts per million (), numerically equivalent to concentration measured in milligrams per litre. One grain per US gallon is approximately . Soft water contains of calcium carbonate equivalents, while hard water contains .