How to use the water hardness calculator
Convert calcium and magnesium to total hardness. Enter calcium, magnesium in the fields above; the total hardness as caco₃, grains per gallon, classification are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- ca — Calcium (mg/L)
- mg — Magnesium (mg/L)
Worked example
With calcium = 60 mg/L, magnesium = 15 mg/L, the calculator gives total hardness as caco₃ ≈ 211.59 mg/L; grains per gallon ≈ 12.37368 gpg; classification ≈ Very hard.
Frequently asked questions
What is the formula for the water hardness calculation?
Total hardness as CaCO₃ (mg/L) = 2.497 × ca+4.118 × mg. Grains per gallon (gpg) = [Total hardness as CaCO₃] / 17.1. Classification = [Total hardness as CaCO₃]<60?"Soft":([Total hardness as CaCO₃]<120?"Moderately hard":([Total hardness as CaCO₃]<180?"Hard":"Very hard")). Here ca is calcium (mg/L), mg is magnesium (mg/L).
What inputs do I need for the water hardness calculator?
You need calcium in mg/L, magnesium in mg/L. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.