What Size Water Softener Should You Get?

How to Size A Water Softener

Water hardness is a common challenge for many homeowners. With a water softener, you can remove excess hardness-causing minerals such as calcium and magnesium, from water.

To eliminate this challenge and improve the quality of your water, here’s everything you need to know about water softeners, including the factors to consider when choosing one.

What is a Water Softener?

A water softener is an appliance that helps remove hardness-causing minerals from water. It utilizes salt, in the form of sodium chloride, to replace the calcium and magnesium minerals, through a process called ion exchange.

A water softener will save you the money you’d ordinarily spend on premature replacement of equipment such as faucet heads, plumbing, and even water heaters. It is a time, energy, and cost-saving investment.

Read More: Pros and Cons of Water Softeners

How to Size a Water Softener Properly

How to Size a Water Softener Properly

Photo: theleader.info

1. Determine Water Hardness Level

When looking for a water softener, determining the water hardness level should be a top priority. It is not advisable to guess the number as this could result in improper softener sizing.

Water hardness is measured in grains per gallon (GPG). Another common measure for hardness, which many municipalities adopt is milligrams per Liter (mg/L). GPG is, however, the preferred standard for determining water hardness.

If you need to convert between the 2 units, use the following formula: 1 GPG = 17.1 mg/L. You can refer to the water hardness standard below, which was established by the American Society of Agricultural Engineers (S-339) and the Water Quality Association (WQA).

Water Hardness Scale




Less than 1.0

Less than 17.0


1 – 3.5

17.1 – 60

Slightly Hard

3.5 – 7

60 – 120

Moderately Hard

7 – 10.5

120 – 180


Over 10.5

Over 180

Very Hard

Source: wqa.org

In case there is iron present in your water, then the hardness level may need correction. For every 1 ppm (part per million) of iron present in the water, you should add 3 GPG to the total hardness value.

If you have a home-based water source, consider using a test kit such as JNW Direct Water Stargazer Set, to determine its hardness.

Note that for water systems that rely on groundwater, hardness can be a major concern since the water is constantly moving across layers of soil and rock. It may dissolve natural mineral and transport them into your water supply.

If you consume city water in your home, your local municipality can provide the exact water hardness level. Some municipalities publish these reports online, making the information easily accessible.

2. Estimate Daily Water Consumption

To accurately calculate consumption, simply examine your water bill to have an idea of the amount of water you use in a month. You can check out multiple monthly bills to help achieve and even more accurate estimate.

You can then use the same information to calculate the average water consumed in your household, daily. In case you don’t have access to water bills and related information, you can still estimate consumption with a fair degree of accuracy.

Another reliable way to determine daily water consumption is to monitor the water meter across a certain period, such as a day or week, to determine the average amount used.

Finally, assuming that the average person uses about 80-100 gallons of water a day, you can calculate the daily water consumption of your household by multiplying this figure by the number of people in your home.

For example, 4 people have a maximum daily consumption rate of 400 gallons (100 x 4). 

3. Calculate Daily Softening Requirement

After obtaining the daily water consumption estimate, proceed to multiply that figure by the water hardness you had obtained in the first step. Ensure the hardness is corrected for iron, if necessary.

The result of this calculation becomes your daily water softening requirement. For example:

Hardness: 10 GPG (grains per gallon),

Daily Water Use: 3 people x 100 gallons/day = 300 gallons/day,

Daily Softening Requirement: 10 x 300 = 3,000 grains per day

Based on the example above, the ideal softener should remove 3,000 grains per day (or 21,000 grains/week). Typically, a softener is sized for a weekly regeneration rate.

4. Calculate Total Grain Capacity

This process is vital because a water softener consistently removes hardness-causing grains until it hits its capacity. At this point, the softener needs to regenerate.

Regeneration is necessitated by saturation of the resin inside the softener, which renders it unable to bind to any additional mineral ions.

The regeneration process serves the purpose of removing minerals and recharging the resin so that the softening process can be initiated again.

Many of the reliable water softeners available today regenerate every 6 to 7 days. And to calculate the total grain capacity, simply multiply the total daily softening requirement you got in step 3 and multiply it by the 7 days that represent a regeneration cycle.

5. Consider Salt-Efficiency

Salt efficiency is defined as the grains of hardness reduced per pound of salt. This approach offers an accurate and honest way to describe a water softener because it accounts for the amount of salt required for resin bed regeneration.

Currently, the NSF/ANSI 44 standard by the National Sanitation Foundation requires a water softener to have a minimum salt efficiency of 3,350 grains/pound. Some municipalities will demand an even higher efficiency of 4,000 grains/pound.

A high-efficiency water softener is one that uses the least amount of salt for maximum resin bed regeneration over a standard interval. That is why experts recommend performing a partial resin bed regeneration, as opposed to 100% regeneration, for your water softener.

A full regeneration is discouraged because it requires more salt, which translates to higher softener running costs. Also, using large amounts of salt for bed regeneration can harm the environment.

What Size Water Softener Should I Get?

What Size Water Softener Should I Get

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When choosing a water softener, do not just rely on the capacity that’s provided by the manufacturer, such as the popular 24,000/32,000/48,000/64,000-grain models available in the market.

For instance, if your household’s weekly removal requirement is 21,000 grains, you may be inclined to choose a 24,000-grain-capacity softener because, in principle, it is the closest match to this demand.

But such sizing that uses grain capacity only is not practical. The more accurate way of sizing a water softener is accounting for its resin (in cubic feet), and the amount of salt (in pounds) needed for regeneration.

What may not be clear from the manufacturer is that it takes about 27 pounds of salt to regenerate a 24,000-grain system fully. This is a massive amount of salt, especially over a long period. A more accurate way of describing a 24,000-grain system is “0.75 cubic feet” of resin.

Dealers thus describe a 32,000-grain system as a “1 cubic foot” system, which would typically require 36 pounds of salt for regeneration. But you can efficiently regenerate this system with only 6 pounds of salt to achieve a 20,000-grain softening capacity.

The efficiency of this system would thus be 3,000 grains/pound (20,000/6), which is higher than the required 3,350 grains/pound, based on the NSF/ANSI 44 standard explained earlier.

Hence, in the case of a 24,000-grain harness removal, you should opt for a 32,000 grain-capacity softener for the best efficiency.


  1. How to Convert Water Hardness in mg/L to GPG – Sciencing
  2. Water Q&A: How much water do I use at home each day? – USGS