Sizing a Water Softener: The Definitive Guide to Water Softener Sizing

How to Properly Size a Water Softener: The Definitive Guide

Do you want to know how to properly size a water softener?

If you’re looking for the definitive guide on sizing a water softener, then this is it. We’ll walk you through everything from what hard water is and why it matters, all the way down to how much money your new system will cost. With our easy-to-use sizing chart, detailed explanation of how softeners work, and simple to use calculations, you can find the perfect model for your needs in no time at all.

We want to help you make the best decision for your home and your family. That’s why we’ve put together this comprehensive guide on how to properly size a water softener.

So, whether you’re just starting to think about getting a water softener or you’re ready to buy one, read on for all the information you need.

You may find my comprehensive guide to water softeners helpful if you’re not familiar with them.

What is Hard Water

Hard water is simply water that contains high levels of minerals, specifically calcium and magnesium. These minerals can cause problems in your home such as:

  • Clogged pipes
  • Scale build-up on faucets, sinks, and appliances
  • Soap scum rings in the bathtub or shower
  • Reduced water pressure
  • Increased use of laundry detergent

Hard water is not a health hazard, but it can cause problems with your appliances and cost you more in energy bills due to scale build-up inside your water heater. It also results in scale accumulation in your pipes, which can decrease your water flow and result in low water pressure.

Depending on where you live, the hardness of your water can vary considerably. Here is a map of water hardness in the United States from the USGS.

US Map of Water Hardness

The following table gives the amount of calcium and grains of hardness in water based on how hard your water is.

Water Hardness Calcium Concentration Grains per Gallon
Soft 10-50 ppm 0-3 gpg
Slightly hard 50-100 ppm 3-7 gpg
Hard 100-200 ppm 7-11 gpg
Very hard 200 ppm and above 11 gpg and above


Measuring water hardness

Hardness is measured in grains per gallon (gpg) or milligrams per liter (mg/L). The higher the number, the harder the water. To get an accurate reading of your home’s hardness level, you will need to have a water test done. You can do it yourself or have a professional test your water for you.

What does grains per gallon mean? It is 1 grain of calcium carbonate dissolved in 1 gallon of water.

How much is a grain? It’s 64.8 milligrams (mg).

You can convert grains per gallon to mg/L by multiplying by 17.1. In other words, 1 gpg is equal to 17.1 mg/L. In case you’re wondering, mg/L is the same as parts per million (ppm).

Sizing a Water SoftenerResidential Water Softener

If you’re considering buying a water softener, you will need to size it correctly. There are many calculators available on the internet that claim to properly size your water softener. Some work well, but others will oversize your system. Most of these online calculators are just a starting point and shouldn’t be used to size your treatment system.

1 – Have a professional do it for you

The best way to size a water softener is to have a professional do it for you. They will take into account your water’s hardness, your family’s water usage, and the flow rate required to serve your needs.

Professionals can also explain the various options and features that you might want to consider when purchasing a water softener. They know what it takes to install a softener in your home and can give you a good idea of installation costs as well as ongoing costs such as salt usage. (Read my article on the cost of installing a water softener.)

A properly sized water softener can save you money by preventing over-saturation and wasting of salt and water. Having a professional do all the work is the best way to get the optimum softener for your home.

Read my article Is Home Depot Water Softener Installation Worth the Cost to learn about what you can expect from professional installation services.

2 – Sizing your water conditioner with rules-of-thumb

If you’re more of a do-it-yourself person, you don’t have to hire a professional (although I highly recommending talking to an expert). A simple method for sizing a water condition is to estimate the size you need using rules-of-thumb.

This method isn’t as accurate as hiring a professional, but it’s the simplest way to determine what size water softener you need. It’s also surprisingly reliable!

Why do rules of thumb work so well? It’s because most people use about the same amount of water each day. We all drink about the same amount of water, we all shower or bathe for about the same amount of time, and we all wash about the same amount of clothes each week.

Here are some very effective sizing guidelines based on the number of people in your home.

1.      1-2 people:  minimum 30,000 grain capacity water softener

2.      3-4 people: 30,000-40,000 grain capacity water softener

3.      4-6 people: 40,000-60,000 grain capacity water softener

These sizing rules have been born out over the years with thousands of water softeners installed and working fine. Your water softener size is important to how effective it operates.

3 – Do-it-yourself approach for designing water softeners

If you’re not satisfied with a ballpark estimate for sizing your water conditioner, then you can follow the same procedures that the pros use. Here is the step-by-step method that water treatment specialists use to determine the water treatment needs for homeowners.

Step 1: Determine your home water needs

The first step in sizing your water conditioner is to determine your water needs. You need to know how much water you use each day so that the water conditioner can produce enough each day. The worst thing you can do is underestimate how much water you’ll need because you’ll end up with partially treated water.

If you’re on city water, then you can review your monthly bill. It should tell you how many gallons of water you used in the last month. I recommend checking an entire year because water usage can vary from month to month and season to season.

If you’re not on city water, then you’ll need to do a little more work. You will need to measure how much water your household uses in one day by taking a reading for a 24-hour period.

If you have a water meter, then you can record the daily, weekly, and monthly usage. Most private water systems don’t have a water meter.

You can estimate your water usage based on how many people are living in your home. On average, each person uses 75 gallons of water each day. For example, 4 people would require 300 gallons per day (4 x 75 = 300).

If you don’t like guestimates, you can calculate how many gallons of water you need based on your specific situation. Using the table below, you can calculate how many gallons per day you use by how you use your water.

Monitor your family’s water usage for each activity, like showering and washing dishes. Then calculate daily volume requirements based on how long and how many times you do each activity.

Plumbing Fixture Amount of Water Used
Faucet 2.5 – 3.0 gpm
Toilet 2.2 – 5.0 gpm
Bathtub 4.0 – 8.0 gpm
Shower 2.5 – 5.0 gpm
Dishwasher 2.0 – 3.0 gpm
Washing Machine 4.0 – 5.0 gpm


Step 2: Measure your water’s hardness

Water Hardness Test Strips
Water hardness test strips are easy to use and provide accurate data.

Water hardness is a measurement of the calcium and magnesium levels in your water. The higher the levels of these minerals, the harder your water will be. Depending on where your water comes from – a public water supply or a private well on your property – you can find out how hard your water is.

Public water – If you’re on public water, call the water department and ask them for the hardness. They test it all the time and have very accurate information

Private well – If you have a private well that supplies your water, you’ll have to measure it yourself.

You can find out how hard your water is by testing it with a water hardness test strip. To measure hardness with test strips, you’ll need to get a sample of your water and follow the strip’s instructions. Essentially, you just dip the paper strip into the water, allow it to react for a minute, and then compare the color to a chart.

Learn more about testing your water and your water softener’s performance in my article.

You can also collect a sample and submit it to a laboratory for analysis. This is the most accurate method to determine how hard your water is. It costs a little money (around $50 per test) and you’ll have to wait on the results, but you’ll know exactly what your water’s hardness is.

Step 3: Calculate grains per day treatment requirement

The next step is to calculate how many grains per day of treatment your water needs. This is done by multiplying the hardness by the flow rate of your water. This information will give you the water softening requirements for your home.

Let’s work through a water softener sizing example. If you need 200 gallons of treated water per day and your water hardness is 12 grains per gallon (gpg), here is what you’ll need.

Daily softening requirement = [200 gallons per day] X [12 gpg] = 2400 grains per day

In plain English, your water softener will remove 2400 grains of hardness from your water every day.

Step 4: Determine correct size of water softener

Once you know how much hardness your water softener has to remove each day, you’ll need to select a unit that can handle the job.

Most water softeners are sized so that they only have to regenerate once each week. Where did this once per week target come from? It’s based on a balance between wear and tear on your equipment with the cost and size of your brine tank.

Every time the water softener regenerates, a series of automatic valves have to open and close. These valves wear out over time, so limiting the number of times they have to cycle will extend the life of your equipment.

You could aim for regenerating less frequently to give you a longer life, but then you’ll need more resin and a larger brine tank. These are the most expensive elements of a water conditioner, and the additional cost is much greater than the cost of repairing a worn-out valve.

To determine what size water conditioner you need, multiply the daily softening requirement by 7 days.

In our previous example, we determined that we need to remove 2400 grains of hardness per day.

Softener Capacity (grains) = Daily softening requirement (gpd) X 7 (days)

Softener Capacity = 2400 gpd x 7 days = 16,800 grains

You should consider this value as the minimum amount required. I recommend adding a factor of safety to account for days where you use more water or variability in your water’s hardness from day to day.

Look for a water softener where 75% of its stated capacity will meet your needs. For our example, you’ll need a unit that can deliver 22,400 grains.

Softener Sizer = [Softener Capacity] / 75% = 16,800 grains / 0.75 = 22,400 grains.

In this example, any water softener that delivers 22,400 or more grains of treatment will work fine. Fortunately, there are a lot of sizes available, and you’ll have no problems finding the right one.

Commonly available water softener sizes include:

  • 24,000 grains capacity
  • 32,000 grains capacity
  • 48,000 grains capacity
  • 56,000 grains capacity
  • 64,000 grains capacity
  • 80,000 grains capacity
  • 96,000 grains capacity

Google Sheets Water Softener Sizing Calculator

If all of these calculations are making your head spin, don’t worry! I created a simple to use calculator that you can use. It’s a Google Sheets spreadsheet that does all of the work for you.

You can enter any of the information that you have, and it will tell you what size water conditioner you need. Home water treatment is much easier with this tool.

Check it out and let me know how you like it.

Importance of Sizing Your Water Softener Properly

As we’ve just reviewed, it takes a little bit of work to properly design a water softener for your home. You may be wondering if it’s worth all the effort.

Properly sizing your water softener is extremely important. You want it to be large enough to provide plenty of water that is adequately softened. You want it small enough to save you money.

Let’s review the impact that having a too large or too small water softener can have on your drinking water and your budget.

Problems of undersizing a water softener

The main reason you’re installing a water softener is to improve the quality of your drinking water, right? If you undersize your softener, you’ll end up with partially treated water. This means that you still have hard water. Why install a water softener if you still have hard water?

This can cause a variety of problems in your home, including soap scum and mineral build-up on dishes, shower doors, and fixtures. You may also see a decrease in the efficiency of your appliances and increased energy costs.

Undersized water softeners can’t handle the full load, so they have to cycle more often. This puts additional wear and tear on your equipment, which shortens its lifespan.

Problems of oversizing a water softener

Water softener salt
An oversized water conditioner will use more salt than is necessary.

What’s wrong with oversizing your water softener? Isn’t bigger better?

An oversized water conditioner will provide you with soft water. That’s the good news.

A larger water condition costs more money to purchase and has higher installation costs. With a larger than necessary unit, you’re paying more money than you need to.

Another consideration is the amount of salt used. Larger units use more salt, even when you take into consideration that it’s removing less hardness. Salt is relatively expensive, especially if you use potassium salt. It’s also heavy – most salt is sold in 40-pound bags – which can be difficult for small people to lift and pour into the brine tank.

You may be interested in my article on water softener salt.

Conduct a water test

Testing your home’s water for hardness is an important step to check the quality of your drinking water. Hard water can damage pipes, appliances, and even your skin and hair. You can test your water using a kit or by getting help from a lab, to know if you need a water softener or treatment to make sure your drinking water is safe and healthy.

Water Softener Sizing Chart

You can estimate the proper size of water softener for your home based on the number of people living there. This chart is a general guideline, and your results may vary based on how much water you use. It’s still a very useful tool. Many people use a water softener sizing chart to select their unit. Others use it as reality check for their calculations.

Regardless of how you use this chart, it’s a valuable tool to ensure that you select the right size water softener.

Water Hardness 1-2 people 3-4 people 5-6 people 7-8 people
5 –  10 gpg 32,000 grains 32,000 grains 32,000 grains 40,000 grains
11 – 20 gpg 32,000 grains 32,000 grains 40,000 grains 48,000 grains
21 – 30 gpg 32,000 grains 40,000 grains 64,000 grains 80,000 grains
31 – 40 gpg 40,000 grains 64,000 grains 64,000 grains 96,000 grains
41 – 50 gpg 64,000 grains 80,000 grains 96,000 grains 110,000 grains
51 – 75 gpg 64,000 grains 80,000 grains 96,000 grains 110,000 grains
76 – 100 gpg 80,000 grains 96,000 grains 96,000 grains 110,000 grains


Sizes of Water Softener

Water Softener Resin
The ion exchange resin removes hardness from water.

Water softeners come in various sizes to accommodate the needs of each application. All water softeners use ion exchange resin to remove calcium and magnesium ions from water. The amount of resin determines how much hardness a particular unit can remove.

Rather than specify water softeners by the amount of resin they contain, their size is stated as grains of treatment capacity. This provides consistency from one type of resin to another.

When you size your water condition, you determine how many grains of softening capacity you need. Every water softener provides this number (grains of treatment) so you can pick the right treatment unit for your needs.

The amount of resin in your water softener is directly related to how many grains it can remove. The more resin, the more treatment capacity it has. This makes perfect sense. This chart shows exactly how much treatment, in grains per day, you should get from various amounts of resin.

Resin Volume Treatment Capacity Salt Required
0.7 cubic feet 24,000 grains capacity 27 pounds
1.0 cubic feet 32,000 grains capacity 36 pounds
1.5 cubic feet 48,000 grains capacity 54 pounds
2.0 cubic feet 64,000 grains capacity 72 pounds
2.5 cubic feet 80,000 grains capacity 90 pounds
3.0 cubic feet 96,000 grains capacity 108 pounds



What size water softener for a family of 3?

A family of 3 will need a 24,000 to 40,000 grain water softener. In general, a 32,000 grain water softener will work fine for 3 people. The two important variables that you need to know are how much water will these people use and how hard is the water. Harder water requires a larger water softener.

What size water softener for a family of 4?

To provide softened water for 4 people, you’ll need a 40,000 grain water softener. A unit as small as 32,000 grains would probably work, but you need to know how hard the water is. If the water is especially hard, a family of 4 might need a 48,000 grain water softener.

What size water softener for a family of 5?

A typical family of 5 would need a 32,000 grain to 56,000 grain water softener. The right size would depend on the amount of hardness in the water. In most applications, a 48,000 grain water softener is ideal for 5 people.

What size water softener for a family of 6?

If you have 6 people in your home, you will need a 32,000 to 56,000 grain water softener. Most families of 6 find that a 48,000 grain water softener is the optimum size. However, hard water may require a 56,000 grain water softener.

Final Take on Sizing a Water Conditioner for Your Home

Hard water can be a pain to deal with. Not only does it leave behind irritating soap scum, but it also causes dry skin and hair. And if you’re using hard well water to cook or drink from your faucet, then this is even more of an issue! Luckily for us, there are ways we can avoid the effects of hard water by installing a water softener in our homes.

Before you purchase a water conditioner, you need to know what size is right for your home.

To help answer this question, we put together this handy guide with everything you need to know about sizing your water softener correctly. We hope it helps!

The Filter Guy

Scott Birch is a water filtration installer and designer. He has worked in the industry for many years and is very familiar with and knowledgeable about residential water treatment equipment. Scott enjoys helping people get the most out of their water filtration systems and ensuring that their homes are getting the best possible quality of water.

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