How to Size a Water Softener 

The proper size of water softener should be efficient and enough to meet the needs of your family. Often, we find that people end up with a water softener that uses too much salt, but it has a small grain capacity.

The secret is in understanding capacity and regeneration efficiency. A water softener should not regenerate every three days or go for 14 days without regeneration. If it takes too long, the resin beads start fouling of iron and sediment and compacting of resin. Seven days between regeneration is what’s best for any water softener.

Factors that affect the Size of Water Softener to Pick

A water softener that is too small suffers from soft water shortages and reduced water shortage while a too big water softener will waste water.

  • Flow Rate 

How many points of use are there in your home? Say three bathrooms, a washer, a dishwasher, four sinks, and three toilets. If they are all used simultaneously, the flow rate will affect how much water each of point of use gets.

Measured in GPM (gallons per minute), the water flow rate is crucial when sizing a water softener. If it cannot sustain the pressure of all the points of use, it results in water shortage.

The best unit will integrate the volume of resin, type of ion exchange, and the internal diameter of the control valve, the bypass valve, the mineral tank, and the distribution system. All these components affect the flow of water.

  • Members in your Household 

How much water does your family consume in a day? Most people use 80-100 gallons of water per day, most of which goes to flushing toilets, baths, and showers. That translates to an average of 320 gallons of water in a day for a household of four, each person using 80 gallons. 

Once you know the amount of water per day, we’ll show you how to integrate that number in water softener sizing.

  • Water Hardness

This is the measure of dissolved minerals which usually includes calcium, magnesium, iron, and manganese. It is measured in grains per gallon (GPG) or milligrams per liter (mg/L). Grains per liter is considered the industry standard.

We can convert Mg/L to GPG by dividing the mg/L value by 17.1. You will want to find the correct hardness value since your water softener controller will need the number so that it can work efficiently. This measure will also include that of iron.

After you find out your water hardness number, you’ll want to add 5 grains for every mg/L or ppm (parts per million) or iron to get the total grain value.

With the grain value of say 10 grains per gallon, you can now multiply this number by the number of gallons that your family uses in a day.

In this case 10 x 320 = 3200 grains of hardness that the water softener has to remove per day. Most water softeners regenerate every seven days. This means it will need to remove 3200 x 7 = 22,400 grains in a week.

Classification of Hard Water

 You can tell if water is soft or hard depending on the above classification of hard water. 

  • Understanding Capacity 

The amount of hardness that a water softener can remove before it regenerates is the capacity of that water softener. Most water softeners are listed from 16,000 grain to a whopping 90,000-grain capacity.

It means that if a water softener is rated at 64,000 grains, it can remove 64,000 grains of hard water grains before the system regenerates. But this is always never the case because the resin is affected by stuff like water pressure, flow rate, and the amount of resin in the mineral tank.

1.5cubic ft of resin beads will usually soften around 30,000 grains of hardness for a model that is rated for 32,000 grains capacity.

Once the water softener reaches its capacity, it will need to regenerate and continue the water softening process. For improved efficiency, it is better to add around 30% of extra capacity when matching your need to the capacity.

  • Water and Salt Regeneration Efficiency 

Water efficiency is the measure of water in gallons that is used in the regeneration process while salt efficiency is the measure of grains of hardness removed per pound of salt used in regeneration. Softeners can be efficiency-rated by the NSF/ANSI standard 44 for Residential Cation Exchange Water Softeners.

Water softeners that use a regeneration on demand can be efficiency rated over those that use a timer regeneration. The efficiency rating is achieved if a water softener can attain the standard of at least 3350 grains of hardness per pound of salt used in the regeneration process. They must also be water efficient at 5 gallons of water per 1000 grains removed.

In the state of California, a water softener is salt efficient if it can remove 4000 grains of hardness per pound of salt.

You will need to understand the amount of resin that is used in the mineral tank and the correct amount of salt that is required per regeneration to get the right capacity and in turn the right size. It’s important to check for grains per pound of salt for the particular water softener you will be buying.

Getting it Right!

Once you find out the number of grains that your water softener needs to remove in a day and a week when it needs to regenerate, it’s time to find the right capacity. Since most water softeners are sized 16,000, 24,000, 30,000, 48,000, and 64,000 grains, it could seem the 24,000-grain capacity could be right in our case of 22,400 grains weekly.

But it takes 27 pounds of salt to regenerate 24,000 grains which is a 0.75 cubic ft of resin unit. Surprisingly, a 32,000-grain system needs 5-7 pounds of salt to remove 20,000 grains of salt in a 1.0 cubic ft resin unit.

Here’s the table to use to gauge efficiency

  • 0.75 cubic ft of resin = 15,000 grains capacity
  • cubic ft of resin = 20,000 grains capacity
  • 1.5 cubic ft of resin = 30,000 grains capacity
  • cubic ft of resin = 40,000 grains capacity
  • cubic ft of resin = 60,000 grains capacity
  • cubic ft of resin = 80,000 grains capacity

In our case of 22,400 grains, we would need a 1.5 cubic ft unit which is a 48,000-grain water softener. Although it is highly priced, you will find that it uses way less salt than the 24,000-grain water softener that is priced less than the 48,000-grain model.

Buying anything smaller means that you may run out of soft water and use lots of salt as it regenerates more frequently than large capacity models.


The best water softener maximizes water softening capacity but minimizes salt, water, and energy usage in the process. After you understand the resulting number of grains to the amount of salt you’ll be using, it will lead to looking for efficiency over the price of the cheapest model you find.

  • May 15, 2019

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