Water Hardness Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Jan 18, 2023

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+)(\mathrm{Ca^{2+}}) and magnesium (Mg2+)(\mathrm{Mg^{2+}}) 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 the hardness of a metallic surface (Brinell hardness number calculator).

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 the hardness of water (in mg/L) can be written as:

Hardness=2.497Cal+4.118Mg\scriptsize \mathrm{Hardness} = 2.497\mathrm{Cal} + 4.118\mathrm{Mg}

where Cal and Mg are amounts of calcium (Ca2+)(\mathrm{Ca^{2+}}) and magnesium (Mg2+)(\mathrm{Mg^{2+}}) in mg/L, respectively.

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

Hardness (mg/CaCO3L\mathrm{mg/CaCO_3L})





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\mathrm{CaCo_3}.

Example: Using the water hardness calculator

Estimate the water hardness of the supply having a calcium concentration of 31 mg/L and a magnesium concentration of 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=2.497 Cal+4.118 Mg=2.497×31+4.118×27=188.6\scriptsize \qquad \begin{align*} \mathrm{Hardness} &= 2.497~\mathrm{Cal} + 4.118~\mathrm{Mg} \\ \scriptsize &= 2.497\times 31 + 4.118\times 27 \\ &= 188.6 \end{align*}

The water hardness value is 188.6 mg/CaCo3L188.6~\mathrm{mg/CaCo_3L}. 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)(\mathrm{CaSO_4})/ calcium chloride (CaCl2)(\mathrm{CaCl_2}) and/or magnesium sulfate (MgSO4)(\mathrm{MgSO_4})/ magnesium chloride (MgCl2)(\mathrm{MgCl_2}).
  • Temporary hardness — Due to the presence of bicarbonate compounds like calcium bicarbonate (Ca(HCO3)2)(\mathrm{Ca(HCO_3)_2}) and magnesium bicarbonate (Mg(HCO3)2)(\mathrm{Mg(HCO_3)_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 — (CaHO3)(\mathrm{CaHO_3}). The idea is to precipitate the compounds out of the solution and then take out the soft water once cooled.

Regular exposure to hard water can lead to scaling in pipes, leading to energy loss in pipes. Learn more about that with our friction loss calculator and pipe flow calculator.


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 measured 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 the 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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