What Size Water Softener Do I Need? Sizing & Grains Guide

Author: Rory Mullan - Published: 2021/07/23 - Updated: 2023/01/05

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Many regions in the US have water with higher mineral content due to geological reasons. Hence, mineral deposits accumulate in pipes, washing machines etc. Also, such water can be harmful to your skin and hair. Luckily, water softeners resolve all these issues.

However, you’re likely to come across a pool of water softeners of varying sizes when purchasing one. Many choices may leave you wondering, “What size of water softener do I need?”

Learn how to select the correct size below which is essential if you want to avoid running into problems.

So, here is our step-by-step guide on how to size a water softener!


This is how to size a water softener to fit your needs:

  1. Have your water tested to determine its hardness level and minerals present.
  2. Make an estimate of your required peak water flow rate.
  3. Calculate how much softened water you need daily.
  4. Compute your total grain capacity requirement between 2 regeneration cycles

(Tip: You should take into account the salt efficiency of a water softener).

How to Size a Water Softener

How to Size a Water Softener Thumbnail

Undersized and Oversized Water Softener Problems

Small water softeners can drastically limit water flow and pressure, are hard to maintain, and sometimes deteriorate without warning.

On the flip side, a giant water softening system may get a little too pricey. Moreover, its irregular regeneration cycles negatively affect the resin bed.

Therefore, accurate sizing is vital, especially if you’re committed to maintaining your water softener yourself.

What Size Water Softener Should I Get?

Here are six things you want to consider to size your water softener properly.

  1. Estimating the Hardness Level of Your Water
  2. Determining Your Daily Water Usage 
  3. Calculating the Amount of Softening You Need Daily 
  4. Calculating the Required Grain Capacity 
  5. Taking Salt Efficiency into Account
  6. Considering Water Flow Rates

We will provide details for each step and give you several examples that will help you determine the right size of water softener that’ll cater to your needs. So, without further delay, let’s get started.

1. Estimating Your Hard Water Level

The first thing you need to know is the exact hardness level of your water; otherwise, you cannot choose the right size water softener.

But what exactly is hard water, or what minerals precisely define hard water?

Well, the amount of calcium and magnesium present inside the water determines its softness or hardness.

You can calculate the amount of calcium carbonate concentration in a few different ways. The levels can be measured either in mg/L (milligram per liter) or gpg (grains per gallon) or ppm (parts per million). Gpg and ppm are most often used to measure the content for commercial purposes.

Calculation Example

1 ppm = 1 mg/L

1 gpg = 17.12 ppm

Explanation: To convert ppm or mg/L to gpg, you’d need to divide it by 17.12.

Hard Water Classes

Here is a chart that classifies water according to its hardness.[1]

Hard Water Classgpgppm (mg/l)
Soft0 – 3.50 – 60
Moderately hard3.56 – 7.0161 – 120
Hard7.06 – 10.51121 – 180
Very hard>10.51>180

You may wonder how you can figure out the hardness level of your water? Well, you have several ways.

  • You can measure the calcium levels in your water using test kits. Several test kits are readily available on the internet.
  • You can ask your water supplier for a quality report of your water.
  • Visit an independent laboratory and get your water tested.

Iron and Manganese

In addition to testing calcium concentrations, you must also check for iron content. For instance, if your water comes straight from a well, it may be higher in iron.

The total hardness value should be increased by 4 gpg for every 1 ppm of iron. The same goes for manganese. Water specialists advise adding 4 gpg for every 1 ppm of manganese in the water.

Calculation Example

Here’s an example of how to calculate that.

If you measure water hardness at 150 ppm, iron at 2 ppm and manganese at 1 ppm, your hard water level is:

150 ppm / 17.12 = 8.76 gpg

8.76 gpg + 8 gpg (iron at 2 ppm) + 4 gpg (manganese at 1 ppm) = 20.76 gpg of total hardness.

2. Determining Your Daily Water Usage

The second step is to determine your daily water consumption. How much water does your family need every day? To get an estimate, you can look at your latest water bill. The bill will accurately show how much water you require every month.

So, you can calculate the volume of water using the information from your bill. Nevertheless, you can multiply the number of people living in your home by 80 gallons if you do not have access to this information.

So, in a family of five, you would approximately need 5 times 80 gallons (400 gallons of water every day).

Alternatively, if your daily water usage is higher, you would have to multiply that number by 100 per household member.

3. Calculating the Amount of Softening Capacity You Need Daily

After successfully calculating water hardness and daily water usage, you need to multiply the hardness level with your daily water requirement.

Calculation Example

For instance, in a family of five people, the daily water consumption will be 5 × 80 = 400 gallons per day.

20.76 hardness grains/gallon × 400 gallons per day = 8304 hardness grains (daily)

So, the above calculation explains that if your water measures 20.76 gpg and your family uses 400 gallons of water per day, your water softener would remove about 8300 hardness grains every day. That’s good enough!

4. Calculating the Required Grain Capacity

A water softener can only eliminate a certain number of hardness grains before it regenerates. Why? It’s just the way the softening process operates. At one point, all resin particles in the softening tank won’t bind more magnesium and calcium particles because they’ll be completely soaked.

Now ideally, a water softener regenerates once a week. This washes out and drains the build-up minerals, and reinfuses the resin bed with salt.

Weekly regeneration cycles result in high softening efficiency at minimum water wastage. Also, it protects the resin bed from fouling.

Calculation Example

Here’s how you can calculate the required grain capacity.

Multiply your softening requirement of 8300 grains by a week, and you’ll get the total softening capacity.

8300 of hardness grains every day × 7 days = 58100 grains (per week)

5. Taking Salt Efficiency into Account

Regenerating the water softener seems to be an easy process so far. It appears that if we soften roughly 58000 grains of hardness each week, we would never run out of soft water. But up to this point, we didn’t take salt efficiency into account.

In other words, regenerating a water softener’s resin bed up to 100% requires a disproportionately high amount of salt. Partial regeneration on the other hand is far more efficient.

To illustrate, a 60,000-grain water softening system may need

  • 5.0 pounds of salt to regenerate 28,000 grains softening capacity
  • 12 pounds to regenerate 40,000 grains
  • And 24 pounds to regenerate the entire resin.

Simply put, while a 60,000-grain unit can eliminate 60,000 hardness grains from water between two regeneration cycles, this would consume a massive amount of salt.

Nevertheless, if you recharge no more than 45% of the resin bed, it would approximately need one-fifth of the total quantity of salt.  Hence, half the total quantity of salt is enough to recharge 67% of the resin. Isn’t it a more efficient way to operate a water softener?

In other words, a higher salt dose results in more softening capacity recharged, but at lower salt efficiency.

In summary: opting for a softening system with more grain capacity than your weekly demand will save you the expense of salt over time. Other advantages include ease of maintenance and less salt discharge consequently reducing environmental damage.

Grains Per Pound of Salt Rating

Whatever water softener model you choose to purchase, ensure that you verify the salt efficiency as measured in grains per pound of salt.

By examining that number, we can see how many hardness grains a water softener can dissolve per pound of salt it uses in an average scenario.

Note that the minimum efficiency of water softener systems installed in California must be 4000 grains per pound.

Also, the water softeners that are NSF/ANSI Standard 44 certified must have a salt efficiency of minimum 3350 grains per pound of salt.

6. Considering Water Flow Rates

trickling faucet

Though daily or weekly softening potential is the main focus, if your water softener can’t produce sufficient soft water during peak usage times, that may be a problem for you.

Especially in the morning when everyone is in the process of leaving for work or school – toilets are flushing, multiple showers are running, and you might be wanting to do dishes before you leave your house – there will be a decrease in flow and leakage of hard water if your water softener is undersized.

Therefore, you have to make sure that the service flow rate of the system you consider buying exceeds required flow rate for your particular home. How?

As a general rule, remember that bigger homes need more water. For example, 7 gallons per minute might do for a single household; however, a flow rate of 20 gpm might be required for a multiple-family home.

One large family might require 15 gpm water flow rate.

Water Softener Sizing Chart

gpg1-2 People3-4 People5-6 People7-8 People

Commercial Softeners: Sizing

For sizing commercial water softeners, you need to consider flow rates, water pressure, water temperature, and a few other factors.

However, this guide is intended for private homeowners interested in installing a water softener in their home and looking for assistance on the correct size. If you’re looking for commercial or industrial applications, we suggest you get in touch with an expert in your area.

What Size Water Softener Do I Need: Calculator

Using a water softener calculator, you’ll be able to determine the accurate size of system that’ll cater to the needs of your household. Here are a few for you to try out:


In conclusion, sizing a water softener the right way is critical to avoid problems down the road.

The process involves 6 steps. First, you measure your hard water level and determine your daily water usage. Then you calculate the amount of softening capacity your need per day and week. Lastly, consider salt efficiency and water flow rates.

Further Reading


Meet Rory Mullan

Rory Mullan Rory has joined the Water Masterz team as a contributing writer. He has covered all sorts of topics in the last several years.

Outside of his writing work, Rory enjoys photographing the Irish landscape and making music!

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