Water Hardness Calculator: What Is Your Water’s Hardness?

Use the above water hardness calculator (or total hardness calculator) to calculate your total water hardness now!

How to Calculate Hardness of Water?

Just enter the hardness of calcium ions (Ca2+) and magnesium ions (Mg2+) into the hard water calculator (or hardness calculator). It will automatically show you the result of total water hardness and your water condition.

How to Read the Water Hardness Calculator: Water Hardness Scale

The hard water calculator will automatically show you your water hardness level and water condition based on the water hardness scale guidelines defined by USGS:

  • 0 to 60 mg/L: Soft Water
  • 61 to 120 mg/L: Moderately Hard Water
  • 121 to 180 mg/L: Hard Water
  • More than 180 mg/L: Very Hard Water

How to Calculate Water Hardness By Using The Formula for Hardness of Water

The total hardness equals the sum of calcium hardness and magnesium hardness and is expressed as calcium carbonate (CaCO3). Below is the water hardness calculation.

The molar mass of CaCO3, Ca2+, and Mg2+ are as below:

  • CaCO3: 100.0869 g/mol
  • Ca2+: 40.078 g/mol
  • Mg2+: 24.305 g/mol

Calcium Hardness Calculation

By dividing the molar mass of CaCO3 by Ca2+, we get:

  • 100.0869 / 40.078 = 2.497

Magnesium Hardness Calculation

By dividing the molar mass of CaCO3 by Mg2+, we get:

  • 100.0869 / 24.305 = 4.118

So, the Formula for Hardness of Water is:

Total hardness = 2.497 (Ca2+) + 4.118 (Mg2+)

  • Mg2+ = Magnesium ion
  • Ca2+ = Calcium ion

Based on the water hardness formula, the number of magnesium ions has a higher weight on the total hardness than the calcium ions.

For example, if your water has a calcium hardness of 30 and a magnesium hardness of 20, by using the water hardness equation, we will get:

2.497 x 30 + 4.118 x 20 = 74.91 +82.36 = 157.27

Your total water hardness is 157.27, which is hard water.

How to Calculate Water Hardness in PPM

The calculation of water hardness in ppm is the same as in mg/L because 1 mg/L equals 1 ppm (parts per million).

How to Calculate Water Hardness in GPG

As 1 gpg (grains per gallon) equals 17.1 mg/L (milligrams per liter), to calculate the total water hardness in gpg, we need to divide the reading in mg/L by 17.1 to get the reading in gpg.

Water Hardness

Hardness in water is mainly due to the dissolved calcium and magnesium mineral compounds, with a smaller amount of iron and heavy metals. The water hardness is measured in milligrams per liter (mg/L), ppm (parts per million), or gpg (grains per gallon).

Type of Water Hardness

There are two types of water hardness: temporary and permanent hardness.

Temporary Hardness

Temporary hardness, also known as carbonate hardness, is caused by the dissolved bicarbonates of calcium and magnesium, carbonate of iron, and heavy metals.

You can remove the temporary hardness by boiling the water as the heat will decompose calcium and magnesium bicarbonate.

Permanent Hardness

Permanent hardness, also known as noncarbonate hardness, is caused by the chlorides and sulfates of calcium, magnesium, iron, and heavy metals.

Unlike temporary hardness, permanent hardness cannot be removed by boiling. You may use water treatment technologies like ion exchange and zeolite softening process.

The total hardness equals the sum of temporary and permanent hardness.

The most common method to remove total water hardness is using a water softening system.

What is Hardness as CaCO3?

According to the guidelines from USGS, the classification of waters based on the calcium carbonate concentration is as below:

  • 0 to 60 mg/L: Soft Water
  • 61 to 120 mg/L: Moderately Hard Water
  • 121 to 180 mg/L: Hard Water
  • More than 180 mg/L: Very Hard Water

Water Hardness Map in the USA

The majority of states in the USA have water hardness problems. Do the water hardness test to double confirm whether your water has a hardness issue.

Water hardness calculator: Water Hardness Map in the USA

How to Test Water Hardness by Using Test Kit Method

Want to test for water hardness?

Follow the steps below to measure your water’s total water hardness concentration.

  1. Buy the water hardness test kit from Amazon or a local store.
  2. Fill up a glass of water for the water hardness test.
  3. Dip the water hardness test strip into your water for 1 second.
  4. Shake and wait for the water hardness test strip for 30 seconds.
  5. Match the color of the test strip to the water hardness color chart.
  6. Record the total water hardness reading in ppm (mg/L) or gpg.

Note: There are many water hardness test strips in the market, but every water hardness tester has different accuracy. So read the review before purchasing.

Water Hardness Problems

The problems caused by hardness are more aesthetic than health concerns.

Hard water has a high concentration of hardness minerals which cause limescale build-up on the surface of your pipes, bathroom floors, water fixtures, and water-using appliances such as water heaters, coffee machines, boilers, and kettles.

Water hardness can affect cleaning by reducing soap lathering, making the cleaning process longer, and using more soap. Hard water also makes clothes wear out quicker.

While hardness minerals may not cause serious health problems, showering with hard water can result in dry skin, dull hair, and weak nails.

What Happens if the Hardness in Water is High?

Water with a high level of hardness may cause the following consequences:

  • Scale forming on plumbing systems and water fixtures reduces water pressure and results in clogged pipes
  • Scale forming on appliances increases the energy consumption of the appliances and reduces their lifespan
  • Make your skin and hair dry, and weak nails
  • The unpleasant taste of the water

Where Does the Hardness in Water Come From?

The hard minerals in your water come from natural sources like ground, rivers, and streams.

How to Remove Hardness in Water

Reverse Osmosis and Ion Exchange are two common and effective technologies to remove calcium and magnesium ions in the water.

A water softener is commonly used as a whole-house solution to remove water hardness by replacing the calcium and magnesium ions with sodium or potassium. In contrast, a Reverse Osmosis System is used as a point-of-use water filtration system to remove water hardness for drinking purposes.


  • https://pubs.usgs.gov/circ/circ1332/includes/circ1332.pdf
  • https://www.usgs.gov/special-topics/water-science-school/science/hardness-water
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