Water Hardness Converter

About this calculator

This tool converts water hardness between the four units labs and manufacturers use: ppm / mg/L as CaCO₃, grains per gallon (gpg) (1 gpg = 17.118 ppm), German degrees (°dH) (1 °dH = 17.848 ppm), and millimoles per liter (mmol/L) of calcium carbonate. Water hardness reflects the dissolved calcium and magnesium content, which affects soap lathering, scale buildup, and the settings needed on a water softener.

Homeowners reading a water utility report, water treatment professionals sizing a softener, and appliance manufacturers specifying compatible water conditions use it to translate a hardness figure from one region's or lab's preferred unit into another. Enter a value in any one unit to see it converted to the rest.