What Size Water Softener Do I Need?

What size water softener do I need

The internet is littered with water softener sizing tools and equations designed to help pick the right sized softener you need. Unfortunately, nearly all of these tools fail to incorporate water softener efficiency, which leads to inaccurate results.

The problem is that you walk away with a softener that consumes massive amounts of salt, instead of a correct model that can save over 500 pounds of salt per year. 

After this guide, you will be able to confidently answer “what size water softener do I need” from our step-by-step sizing process.   

How to Properly Size a Water Softener

The key to sizing a water softener is balancing your home’s water quality, hardness, and water usage with a sufficiently sized system that maximizes soft water capacity while minimizing salt use.  Here is how to size a water softener for your needs:

  1. Water Hardness Level
  2. Water Consumption
  3. Number Of People
  4. Daily Softening Requirements
  5. Grain Size Requirements

We will discuss each step in detail below and provide examples along the way so everything is simple to understand.

Water Hardness Level

Water Hardness is the amount of magnesium and calcium that is dissolved in your water.  Grains per gallon (GPG) is the most common way to measure water hardness. For example, one grain of water hardness is equal to 1/7,000 of a pound.

Water can be classified as soft, slightly hard, hard, very hard [1]:

ClassificationMilligrams/LiterGrains/Gallon
Soft0 – 17.10 – 1
Slightly Hard17.1 – 601 – 3.5
Moderately Hard60 – 1203.5 – 7.0
Hard120 – 1807.0 – 10.5
Very Hard180 and over10.5 and over

It is critical to know your water hardness when considering water softener options to purchase. If not, you can end up with the incorrect sized softener.  Additionally, your softener will request the hardness value when it’s time for setup programming.

There are few ways to determine the water hardness at your home.  If you have municipal or city water, you can get the approximate hardness level from your water utility reports.  

If you have a private well, you will need to test your water hardness. Since iron is common in wells, you need to adjust the hardness level for the presence of iron. For every 1 part per million (PPM) of iron, 4 GPG of hardness needs to be added to the total value.

To Convert PPM to GPG, divide by 17.2.  So if you have a hardness reading of 100 PPM, and iron at 1 iron PPM, here is how to calculate it: 

100 / 17.2 = 5.8 GPG and 5.8 + 4 = 9.8 GPG total hardness. 

Water Consumption

The next step in determining water softener sizing is to calculate your home’s total water consumption. The best way to get this is to look at a water utility bill that shows total consumption over the last month. You can then use this number to figure out how much water your household uses on average per day. An alternative is to simply multiply the number of people living in the home by 100 gallons per day, which is the USGS estimate of water usage per person.

If you need to see what size water softener for a family of 4, you can multiply 4 x 100 = 400 gallons of water consumption per day. 

Calculate Daily Softening Requirements

The third step to size a water softener is to calculate your daily water softening requirements.  Take the water hardness level and multiply that by the daily water usage to get grains per day you will need.  

Using the examples from step one, we have total water hardness of 9.8 GPG and water consumption of 400 gallons. The daily softening requirements are 9.8 x 400 = 3,920 grains per day. 

With this example, the softener will remove 3,920 grains per day. 

Grain Size Requirements

A water softener can only treat so many hardness grains before it needs to regenerate. A salt-based water softener uses the process known as ion exchange to remove calcium and magnesium ions.  In this process the resin beads eventually become saturated and need to be flushed clean to remain effective.  

Regeneration involves rinsing and draining away the accumulated minerals in what’s known as brine water. The resin bed is then recharged with sodium or potassium.  Keep in mind a softener will typically regenerate around once per week.  This strikes an ideal balance between softening efficiency and reduced waste water. 

Taking the daily softening requirement of 3,920 grains and multiplying it by 7 days, we get a total softening capacity of 27,440 grains per regeneration cycle. 

Does Softener Efficiency Matter?

The efficiency of your water softener determines how much salt you need to purchase, the amount of waste water used, and the amount of salt gets drained into the environment. Over the lifespan of the water softener, this can translate to significant cost savings and low maintenance requirements.

What Size Water Softener Do I Need_Grain and Salt Efficiency

In general, the higher amount of salt used means a higher softening capacity, but a lower efficiency per pound of salt.

Therefore, if you require a water softener that can remove 27,4400 hardness grains per regeneration cycle as calculated in our example above, using a system with a higher grain capacity like 40,000 grains will save a lot on salt over the softener’s life.

Properly sizing a softener and considering its efficiency will make sure you purchase a softener that doesn’t run out of soft water but also uses the least amount of salt as possible. 

Water Softener Size Chart

Knowing your water and usage is critical to purchasing the ideal water softener for your needs. A system that’s too small will not be able to provide enough soft water and will wear down quickly. Higher grain water softeners can cost more money and may not be necessary.

See the chart below to determine the best water softener based on your hardness, size of family, grain capacity, and tank size.

Hardness GPGNumber Of PeopleResin Cubic RootGrain CapacityTank Size
0 – 5 GPG1 – 20.7515,0008″ x 46″
6 – 10 GPG1 – 21.020,0009″ x 48″
5 – 10 GPG2 – 41.530,00010″ x 52″
11 – 20 GPG4 – 62.040,00012″ x 52″
21 – 30 GPG6 – 73.060,00013″ x 54″
31 – 40 GPG7 – 84.080,00014″ x 65″
Water softener size chart & grain chart

Why Trust Freshnss?

Ricky is the founder of Freshnss and product reviewer specializing in water filtration, home, and kitchen products. For this review, he spoke with our water review board of experts. And also with our network of industry professionals who offered recommendations on how to size a water softener. Next, he researched today’s water softeners, considering dozens of options from various merchants and retailers. He has read thousands of user reviews, and written hundreds of product reviews. He has also tested and re-tested some of our top picks, and looked for filtration companies for new home water treatment options worth trying.

Article Sources

Freshnss uses only the highest-quality sources to support the facts used in our articles including: government organizations, independent studies, peer-reviewed journals, and lab testing results. Read our editorial review guidelines here to learn more about how we verify and fact-check our writing to keep our content reliable, accurate, and trustworthy.

  1. Drinking Water Treatment: Salt-Free Water “Softener” Option, University Of Nebraska Lincoln
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