Water Hardness Calculator

Work out water hardness instantly with clear inputs, formula shown and shareable results.

About Water Hardness Calculator

Hardness is expressed as calcium carbonate equivalent: calcium multiplied by 2.497 and magnesium by 4.118, being the ratios of calcium carbonate's molar mass to each element's equivalent. Carbonate hardness is the part balanced by alkalinity and removable by lime; the remainder is non-carbonate and needs soda ash or ion exchange.

Formulas

Hardness as CaCO3

Total hardness = Ca x 2.497 + Mg x 4.118

Split

Carbonate hardness = min(total hardness, alkalinity); non-carbonate = total - carbonate

Worked example

With the default values below, Water Hardness Calculator returns Total Hardness of 302.710. Change any input above and every figure here is recalculated in your browser.

Inputs used

Calciumminimum 0 mg/L as Ca: 80 mg/L as Ca
Magnesiumminimum 0 mg/L as Mg: 25 mg/L as Mg
Total Alkalinityminimum 0 mg/L as CaCO3: 150 mg/L as CaCO3
Water Volumeminimum 0 m3: 1,000 m3

Results

Total Hardness: 302.710
Carbonate Hardness: 150.000
Non-Carbonate Hardness: 152.710
Hardness Classification: Very hard

Step by step

1Values used
2Hardness as CaCO3
3Split
4Total Hardness= 302.710
5Carbonate Hardness= 150.000
6Non-Carbonate Hardness= 152.710
7Hardness Classification= Very hard

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does the split matter?

Because the treatment differs. Carbonate hardness precipitates with lime alone; non-carbonate hardness needs soda ash, which is more expensive and adds sodium and sulphate to the treated water.

Is hard water a health problem?

No, and there is some evidence of cardiovascular benefit. It is an aesthetic and economic issue: scale in pipes and heaters, and increased soap and detergent consumption.