Water Hardness Calculator Widget

Calculation mode

Start by calculating total hardness from calcium and magnesium, or switch modes once you already know hardness in grains per gallon.

Calcium (mg/L) (required) Enter calcium as Ca²⁺ from a lab report or test kit, in mg/L or ppm.

Magnesium (mg/L) (required) Enter magnesium as Mg²⁺ from a lab report or test kit, in mg/L or ppm.

Alkalinity as CaCO₃ (optional) Optional. Enter total alkalinity as CaCO₃ to estimate temporary and permanent hardness.

Known hardness (gpg) (required) Enter total hardness in grains per gallon for the softener sizing estimate.

Daily water use per person (required) Use your water bill if available; otherwise 75–100 gallons per person per day is a common household planning range.

Household size (required) Number of people whose daily water use the softener will serve.

Answer 136.8 mg/L as CaCO₃ · Hard

Total hardness 136.8 mg/L as CaCO₃

Grains per gallon 7.99 gpg

German degrees 7.67 °dH

French degrees 13.68 °fH

Hardness category Hard (121–180 mg/L as CaCO₃)

Temporary hardness Enter alkalinity to split

Permanent hardness Enter alkalinity to split

Practical note Scale control or softening is often worth evaluating.