Do you live in a community with hard water? And are you thinking about purchasing a water softener?  But maybe you’re a little unsure about which size is best suited to your needs.

You’re not alone.  In many places in the U.S. and throughout the globe, water softeners are used by households and industry in order to filter out high concentrations of minerals (typically calcium and magnesium) and get purer, cleaner, and better-tasting water.  

But how do you know how to size a water softener?  Not to worry.  In this brief article, we discuss a simple, straightforward way of figuring out what size water softener is best for you.  In a nutshell, it depends on the hardness of the water that you’re softening, the amount of water being consumed, and the efficiency of the unit itself.

What Is A Water Softener

Let’s start by quickly reviewing water softening.  The purpose of a water softener is to treat water that has become saturated with high mineral levels (usually calcium and magnesium).  

When water passes through certain rock formations like chalk, gypsum, or limestone, it takes on higher levels of magnesium and calcium, and the result is called ‘hard water.’  As you might expect, communities that source their water from groundwater are more likely to have hard water.  While hard water is usually safe to drink, it can lead to a variety of adverse effects for you and your home.

For instance, hard water can dry out your skin and hair, as well as leave behind a mineral ‘film’ on your body after bathing.  This can cause brittle damaged hair and irritated skin.  Similarly, prolonged use of hard water can lead to limescale build up around the bathtub, and in appliances like the coffee machine, dishwasher, kettle, and hot water tank.

In addition, some folks simply don’t like the look and taste of hard water when compared to its softer counterpart.  Because of these frustrating side-effects of living with hard water, many people chose to invest in a water softener.  

According to data from the U.S. Geological Survey, hard water is most prevalent in the Midwest and Southwest regions in the U.S., but it is not limited to those areas.

A water softener system uses a process called ion exchange to remove excess calcium and magnesium from water. At its core, water softeners simply run hard water through resin beads which attract and absorb the mineral content.  The calcium and magnesium are then replaced with sodium, and softer water flows out of the system and into your house.

Why Size Matters

OK, so you’ve figured out that you have hard water, and you’ve decided that you need to invest in a water softener.  Now it’s a matter of choosing the right size model.  

Size matters because you want your investment to be effective while still maintaining a good bang for your buck, and that means purchasing a softener tailored to your softening needs.  Getting a softener with a capacity that is too small will mean that you’re unable to soften all the water your household needs to run smoothly.  And getting one that is too big will mean shelling out more cash than is really required.  

Let’s explore how to properly size a water softener.  The two main considerations are:


How much water does your household use per week?


What is the hardness level of the water you are softening?

Water Consumption 

Let’s start with the first on our list, total household water consumption.  What we are trying to figure out is how much water our household uses over a given period of time, usually a month or week.  In some places, you might receive a water bill that estimates your total water consumption for the month.  This is typically the most accurate measurement possible.

If you don’t have access to a precise measure, a quick shortcut is to simply multiply the number of people living in your home by 80 gallons.

The national average range is 80-100 gallons per day.

So for a family of 4, we multiply 80 x 4 = 320 gallons per day.  If you have reason to believe your house uses more water than average, you can multiply by 100 to be safe.  

Water Hardness

The level of hardness in water is typically measured in grains per gallon (gpg), parts per million (ppm), or milligrams per liter (mg/L).  For reference, 1 gpg is equal to about 17.1 mg/L or 17.1 ppm. 

To measure the hardness of your water, you can contact your local water supplier or community health authority.  Alternatively, you can purchase a water hardness test kit, which can be the only option if you’re using a private water source like a well.

A mild water hardness level, in the 1-3 grain per gallon range, means there is some, but fairly little dissolved calcium and magnesium in your water.  Alternatively, water that is considered very hard has 7-10 grains per gallon.  

Let’s do a full calculation together.  If we’re living in a 4 person household and we each use roughly 80 gallons of water per day, we get to 320 gallons of total daily water use.  

If our water is quite hard, around 8 grains per gallon, then we would multiply 320 x 8 to get 2,560 grains as our daily softening requirement.

Water Softener Regeneration

Now that we have a sense of our daily softening requirement, we can start looking at water softeners with different capacities, to see which fits our needs best.

Before going out and shopping though, keep in mind that most manufacturers design their units with a regeneration cycle of about 1 week.  Units are thus usually marketed as having 24,000, 32,000, or 48,000 grain capacity, referring to the total number of grains they can remove from hard water in between regenerations.

What’s a regeneration cycle?  Glad you asked!  After a while, the softener has trapped all the hardness minerals it can handle and becomes saturated.  At that time, it needs to be flushed out and cleaned such that it can continue to soften new water.  

This matters when we’re trying to size our softener because the machine needs to be kept on schedule to remain efficient.  If we don’t regenerate the unit at the appropriate time, it won’t work as well going forward.

Accordingly, if we know our softener needs to regenerate every 7 days, we can multiply our daily softening requirement, which if you can remember from our example is 2,560 x 7 = 17,920.  This is our final number, our required capacity in between regenerations.  

For reference, families of 4 or 5 will typically use a 24,000 or 32,000 grain capacity water softener, depending on the specifics of their situation. 

Water Softener Efficiency

One last point on water softener efficiency and size is worth mentioning.  Efficiency refers to the amount of salt required to run your water softener at its maximum capacity.  

Efficiency is important to keep in mind because oftentimes a lot of salt is needed to run a softener at its full capacity, and so you can potentially benefit by purchasing a softener that has the ability to filter out more total grains than you require, but you’re then buying less salt.

In other words, it might be beneficial to invest in a larger softener, even though it’s more expensive up front, knowing that you will be able to save on salt costs down the line.  Over the entire lifespan of a water softener, buying a higher salt efficiency softener will save you time and money.

Let’s explore an example.  If you have weekly softening requirements of about 20,000 grains, you may think that a 24,000 grain unit would be perfect for you.  However, it will take a large amount of salt, usually in the neighborhood of 25 pounds per week, to keep the machine running at its full capacity.  

However, using less salt in a larger machine, say about 5-6 pounds of salt in a 32,000 grain machine, will still get you about 20,000 grains of softening.  This is because larger capacity machines have more resin, and thus even when they operate with less salt, they can still provide plenty of water softening.

Using the least amount of salt possible, a softener with 1 cubic foot of resin will have about a 20,000 grain capacity, a softener with 1.5 cubic feet will have about a 30,000 grain capacity, and 2 cubic feet of resin will yield approximately 40,000 grains.

So be sure to keep an estimate of your long term costs in mind – how much salt you’ll be buying, how frequently and for how long – before you purchase a softener with the lowest capacity to meet your needs.

Sizing A Water Softener

We hope the steps outlined above are useful in helping you pick out the right size water softener for your home, and in your journey to combat all the frustrations and nuisances of living with hard water.  Happy water softening!