Water Hardness Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Jun 30, 2022

The water hardness calculator is the tool you need to estimate the amount of dissolved minerals present in your tap water supply. Minerals like calcium (Ca2+) and magnesium (Mg2+) are often present in your regular water supply. They often have health benefits, however, they can also cause issues like scaling in pipes, boilers, and heaters clogging and/or reducing the efficiency of the apparatus. Read on to understand how to calculate the hardness of the water.
It is important to remember that the water hardness is different from hardness of a metallic surface.

What is water hardness?

Water hardness is the parameter used to measure the dissolved minerals like calcium and magnesium in water. Based on the value of water hardness, water is classified as hard or soft. Hard water is common in the areas where gypsum, limestone, and chalk are found in the ground. The hardness of water is measured in the units mg/L (milligrams per liter), ppm (parts per million) or mmol/L (millimoles per liter). The formula to calculate hardness of water (in mg/L) can be written as:

Hardness = Cal * 2.497 + Mg * 4.118

where Cal and Mg are amounts of calcium (Ca2+) and magnesium (Mg2+) in mg/L, respectively.

Based on the value of hardness, the water is categorized as hard or soft:

Hardness (mg/CaCO3L)
Moderately hard
very Hard

How to calculate the hardness of water using this calculator?

To calculate the hardness of water, follow the steps below:

  1. Enter the value of calcium concentration in mg/L.
  2. Enter the value of magnesium concentration in mg/L.
  3. The water hardness calculator will now return the hardness value in mg/L of CaCo3.

Example: Using the water hardness calculator

Estimate the water hardness of the supply having calcium concentration as 31 mg/L and magnesium concentration as 27 mg/L.
To estimate the hardness of water:

  1. Enter the value of calcium concentration as 31 mg/L.
  2. Enter the value of magnesium concentration as 27 mg/L.
  3. Using the water hardness calculator:
    Hardness = Cal * 2.497 + Mg * 4.118
    Hardness = 31 * 2.497 + 27 * 4.118 = 188.6

The water hardness value is 188.6 mg/CaCo3L. Based on the hardness scale, the water is very hard.

Types of Hardness

There are two types of water hardness — temporary and permanent. The classification is based on the presence of different metallic compounds.

  • Permanent hardness — Contains calcium sulfate (CaSO4)/ calcium chloride (CaCl2) and/or magnesium sulfate (MgSO4) / magnesium chloride (MgCl2).
  • Temporary hardness — Due to the presence of bicarbonate compounds like calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2).

Permanent hardness can be removed by boiling the water or running the water through an ion-exchange column, whereas temporary hardness can be removed by boiling the water or using lime (calcium hydroxide — Ca(HO)3). The idea is to precipitate the compounds out of the solution and then take out the soft water once cooled.


What is hardness of water?

Hardness is the parameter about water that tells us about the concentration of magnesium and calcium ions in the water as different compounds like magnesium sulfate/bicarbonate and calcium bicarbonate/chloride.

What are the units of water hardness?

Water hardness is measures in the units mg/L or parts per million (ppm).

How do I calculate water hardness?

Water hardness can be calculated by the following steps:

  1. Multiply the calcium ion concentration by 2.497.
  2. Multiply the magnesium ion concentration by 4.118.
  3. Add the two numbers to obtain the water hardness in mg-CaCo3/L.

The formula to calculate hardness of water is:

Hardness = Cal × 2.497 + Mg × 4.118

What is the range of hardness value for soft water?

The water is regarded as soft if the hardness value for water remains under 60 mg/L.

Rahul Dhari
Calcium content
lbs/US gal
Magnesium content
lbs/US gal
Water hardness
lbs/US gal
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