Water Hardness Calculator

Primary output 136.8 mg/L as CaCO₃ · Hard

Start with calcium and magnesium from a water test. Add alkalinity only when you need a temporary/permanent split, or switch modes once you already know hardness in gpg.

Calculation mode

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

Enter calcium as Ca²⁺ from a lab report or test kit, in mg/L or ppm.
Enter magnesium as Mg²⁺ from a lab report or test kit, in mg/L or ppm.
Enter total hardness in grains per gallon for the softener sizing estimate.
Use your water bill if available; otherwise 75–100 gallons per person per day is a common household planning range.
Number of people whose daily water use the softener will serve.
Advanced options
Optional. Enter total alkalinity as CaCO₃ to estimate temporary and permanent hardness.
Answer 136.8 mg/L as CaCO₃ · Hard
Total hardness 136.8 mg/L as CaCO₃
Grains per gallon 7.99 gpg
Hardness category Hard (121–180 mg/L as CaCO₃)
Show calculation details
German degrees 7.67 °dH
French degrees 13.68 °fH
Temporary hardness Enter alkalinity to split
Permanent hardness Enter alkalinity to split
Practical note Scale control or softening is often worth evaluating.