Enter the concentration and volume into the calculator to determine the hardness of water. This calculator can also evaluate any of the variables given the others are known.

Water Softener Hardness Formula

The following formula is used to calculate the hardness of water using a water softener. 

H = (C * V) / 17.1

Variables:

  • H is the hardness of water (grains per gallon or gpg)
  • C is the concentration of calcium and magnesium ions in water (parts per million or ppm)
  • V is the volume of water passing through the water softener (gallons) 17.1 is a conversion factor to convert ppm to gpg

To calculate the hardness of water, multiply the concentration of calcium and magnesium ions in water by the volume of water passing through the water softener. Then, divide the result by 17.1 to convert the hardness from parts per million to grains per gallon.

What is a Water Softener Hardness?

A water softener hardness refers to the amount of dissolved calcium and magnesium in the water, which are the minerals that make water “hard.” These minerals can cause scale build-up in pipes and appliances, making them less efficient and potentially shortening their lifespan. A water softener removes these minerals, reducing the hardness of the water and preventing these issues. The level of hardness in water is usually measured in grains per gallon (gpg), with anything over 1 gpg generally considered hard water.

How to Calculate Water Softener Hardness?

The following steps outline how to calculate the Water Softener Hardness.

  1. First, determine the concentration of calcium and magnesium ions in water (C) in parts per million (ppm).
  2. Next, determine the volume of water passing through the water softener (V) in gallons.
  3. Next, gather the formula from above: H = (C * V) / 17.1.
  4. Finally, calculate the Water Softener Hardness (H) in grains per gallon (gpg).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

concentration of calcium and magnesium ions in water (C) = 120 ppm

volume of water passing through the water softener (V) = 50 gallons