Water hardness is a measure of the concentration of hard ions (i.e. calcium and magnesium) in your water supply. Water hardness is important because it has a direct impact on how well soap and detergents work, as well as how long they last before needing to be replaced or recharged (by adding more soap).

In this article, we’ll define what water hardness means, what causes it, how you can calculate it using this calculator, and give you some examples of common uses for water hardness information along with their applications in day-to-day life!

What is water hardness?

Water hardness is a measure of the concentration of hard ions (i.e., calcium and magnesium) in your water supply. The two most common units used to express hardness are grains per gallon (gpg) and parts per million (ppm). Grains refer to the actual weight of calcium carbonate per volume, while ppm refers to the number of milligrams of calcium carbonate dissolved in each liter of the water sample.

If you’re measuring your water’s hardness in gpg, then start by taking your reading with a grain test kit like this one or this one from Amazon; if you’re measuring it in ppm, then grab yourself a multimeter like this one from Amazon or another place online such as eBay or Craigslist.

How to calculate the hardness of water using this calculator?

The calculator is based on the equation below:

\text {Hardness} = 2.497 \text { (Ca)} + 4.118 \text { (Mg)}

Where Ca and Mg are concentrations of calcium and magnesium ions in milligrams per liter.

The values for Ca, Mg, and water hardness can be obtained from your local water authority or by using a TDS meter.

Example: Using the water hardness calculator

To use the calculator, enter the hardness of your water (measured in grains per gallon, or gpg), how much water you use each day, and how much soap you use. The calculator will tell you how much salt to add to remove a given amount of hardness from your water. For example, if you have 2 grains of hardness in 1 gallon of water for every 5 gallons used during a shower or bath, but only add 1/2 teaspoon of soap for every 5 gallons used by washing dishes or laundry (including all other household uses) then:

  • You need 1 pound (.5 kg) of salt for every 2 gallons used on average per day
  • 1 pound is equal to 0.45 kilograms

This means that if you were using 4 pints (or 3 quarts) while taking two baths and washing two loads of laundry per week (8 pints total), then the recommended dosage would be 8 pounds (3 kg) per month!


What is water hardness and why is it important?

Hard water is richer in minerals than soft water and tends to have a high content of calcium and magnesium because it has dissolved the compounds present in sedimentary rock.

Is it better to have hard or soft water?

Many people believe that soft water offers a better cleaning for your body and your home because it doesn’t leave behind a mineral residue like hard water can. But the truth is that neither type of water offers a better or worse clean.

What is a good hardness level?

The rule of thumb is that a good hardness level should not be higher than 120 to 170 mg/L, i.e., seven to ten grains per gallon of water.