What Size Water Softener do I Need?

Updated on:
January 6, 2024

There are several benefits to having a water softener in your home, but the process of finding the best system can be complicated. Which size do you need? How many grains do you need? What type of water softener is optimal for your needs?

Read on to find out everything you need to know about how to size a water softener.

Factors to Consider

If you’re in the market for a water softener, you’ve likely observed that they come in various sizes. However, in order to determine which size is best for your home, you need to consider the following factors:

1. Your water hardness level

Your water hardness is a measure of the levels of magnesium and calcium in your water supply. This value is represented using three distinct units of measurement. The first unit is milligrams per liter, abbreviated as “mg/L,” and then there’s parts per million (PPM). However, grains per gallon, or GPG, is the industry standard unit for measuring water hardness. The word “grains” refers to the amount of hard minerals in the water.

If you want to convert from mg/L or PPM to GPG, all you need to do is divide by 17.12.

For instance, 1 PPM = 1 mg/L and 1 GPG = 17.12 PPM or 17.12 mg/L

The chart below shows the general classification of water hardness levels:

Classificationmg/LPartGrains per gallon
Moderately hard61–12061–1203.56–7.01
Very hard>180>180>10.51

It is crucial that you get an accurate water hardness reading. Otherwise, you may end up purchasing an oversized water softener, which could cost you more salt in the long run. If you are on a municipal water supply, most local water authorities tend to post the local water hardness levels in their annual reports. If you have a well, a professional water-quality test is required.

You must be aware of excess iron levels, especially if you get your water from a well. Add 4 GPG to the overall hardness value for every 1 PPM of iron. Some experts advise adding 4 GPG per 1 PPM of manganese.

How to calculate your water’s hardness (measured at 140 PPM and iron at 1 PPM)

144 PPM ÷ 17.12 = 8.18 GPG

8.18 + 4 GPG (same as iron at 1 PPM) = 12.18 GPG 

Your total hardness value is 12.18 GPG

2. Your average daily water consumption

Knowing how much water your home consumes on a daily basis is also a useful starting point for calculating the ideal water softener capacity. Your local water company should be able to provide information about your average water use over time. You can use it to determine a general estimate of your household’s daily water consumption. 

If you do not have access to this information, you can multiply the number of people who reside in your house by 80–100. This is the amount of water that the United States Geological Survey (USGS) claims the average person uses daily. If you like taking really lengthy showers, multiply by 100. If you are good at preserving water, multiply by 80. That’s around 320 gallons a day. Alternatively, you can find a water treatment specialist who can do a thorough evaluation of your household’s daily water consumption.

3. Your flow rate

If your softener cannot generate enough soft water during high-demand periods, hard water will seep through and the water pressure will decrease.

This is especially true in the morning, when everyone is getting ready for work and school and there are a couple of showers and faucets running, toilets are flushing, and you’ve probably started the dishwasher before leaving for the school run. Therefore, before you figure out what water softener size you need, pay close attention to service flow rates, which are measured in gallons per minute (GPM). 

According to Pennsylvania State University, one person in the home uses between 50 and 100 gallons of water per day (that’s 200 to 400 gallons per day for a family of four). It is recommended that a water system be able to meet all of the day’s expected water needs during a two-hour peak demand period. 

If you think your home can use 400 gallons of water a day, the water system should be able to provide adequate pressure to last two hours.

The chart below shows the amount of water that common household appliances consume:

ApplianceWater use
Water softener regeneration50–100 gallons per cycle
Dishwasher7–14 gallons per load
Washing machine27–53 gallons per load
Kitchen sink3 GPM
Shower or tub5 GPM
Toilet5 gallons per flush

4. Your water-softening needs

To figure out how much softening you need each day, multiply the amount of water you use each day by the total hardness number. Let’s say your water hardness is 12.18 GPG and your family of four uses an average of 400 gallons of water per day—400 multiplied by 12.18 GPG equals 4,872 GR, which is the number of grains your water softener will be required to remove every day.

5. The water-softener capacity

When describing the capacity of their water softeners, manufacturers refer to the amount of grain the system can remove before regeneration is required. Typically, model sizes are advertised in terms of grain capacity (GR), with the most popular options ranging from 24,000 to 80,000 GR.

During the regeneration process, deposited minerals are washed and drained away, and the resin bed is recharged with salt or potassium. A majority of specialists recommend that regeneration occurs every 6–7 days.

This strikes a nice balance between high softening efficiency, minimal wastewater generation, and head-valve wear protection. Additionally, it will preserve the resin beads by shielding them from iron and silt.

The decision should be fairly straightforward, right? Returning to our previous example, a home with a daily softening demand of 4,872 grains should choose a system with a grain capacity of 35,000 grains in order to meet its softening requirement of 34,104 GR with one regeneration cycle per week.

However, it’s not that simple. Manufacturers’ grain capacity claims are usually inaccurate. They describe the maximum number of hardness grains that can be removed under ideal lab circumstances, not the number of grains that can be removed before the regeneration process is required in typical usage.

When doing your calculations, the industry norm is to aim for 30% more capacity than your calculations show is necessary.

In other words, if your weekly softening demand is 34,104 grains, you need to add an extra 6,804 grains and get a machine with a minimum advertised capacity of at least 41,000 grains. This will save you a substantial amount of money on future salt purchases.

In addition, servicing will be far more convenient, and less salt will be released into the environment, reducing the threat to aquatic life.

To clarify, you need a water softener with a higher grain capacity than estimated because your softener will deplete faster if you do not allow it to regenerate to 100%. A larger system can compensate for this effect.

Grain capacity can also be described as cubic feet of softening resin. Higher volume means a larger tank size. The following table can be used to decide what size water softener you should install:

Resin in cubic feet (cu. ft.)Tank dimension (diameter x height)Maximum grain capacity
0.758″ x 44″15,000
1.09″ x 48″20,000
1.510″ x 54″30,000
2.012″ x 52″40,000
2.513″ x 52″50,000
3.014″ x 65″60,000

6. Salt-efficiency levels

Always examine a model’s salt efficiency, which is indicated in grains per pound of salt. The figure represents how many hardness grains a water softener can remove per pound of salt used at the lowest salt dosage and under real-world settings.

One model may have 4,410 GR at 2.9 pounds and another 5,060 GR at 2.7 pounds. The latter is more efficient. Softeners certified to NSF/ANSI Standard 44 must have a salt efficiency rating of at least 3,350 grains per pound of salt, so keep an eye out for that. Systems installed in California must have an efficiency of at least 4,000 grains per pound.

Types of Water Softeners

In addition to the question of how to size a water softener, you should also find out what type of water softener you should get for your home.

There are three primary types of water softeners: ion-exchange, dual-tank, and salt-free water softeners. Each type offers its own set of advantages as well as reasons why it may not be suitable for your situation. Let’s take a closer look at each type:

Ion-exchange water softeners

When it comes down to it, all water softeners operate on the basis of ion exchange. This is the mechanism through which calcium and magnesium ions are exchanged for sodium chloride or potassium ions. To keep it simple, single-tank salt softeners (also called a grain water softener) are referred to as ion-exchange systems. Some of the advantages of ion-exchange water softeners are their compact size, lower cost, and ease of installation. One possible disadvantage is that soft water is unavailable for use during regeneration.

Dual-tank water softeners

Dual tank systems operate two water softener tanks at the same time. These provide the home with soft water all day, every day. When one tank needs to regenerate, the second tank takes care of your water demands. They are not considered necessary in a single-family residence. Dual-tank units, on the other hand, may make life considerably easier in multi-family homes or on commercial properties. These softeners are often more expensive due to their large size.

Salt-free water softeners

When it comes to softening water, salt-free softeners don’t perform as well as you might hope. Rather, these systems, really water conditioners rather than softeners, keep pipes free of mineral buildup. These softeners do not remove hardness from the water. Instead, they protect the plumbing system against damage. That means you’ll still have to spend more money on a separate filtration system. That’s why it’s not commonly advised to install a water softener like this in residential settings.

What Size Water Softener Do I Need: Final Thoughts

You might feel overwhelmed trying to choose a water softener for your home, but you don’t need to be.

The afore-mentioned factors will go a long way toward helping you determine the best size water softener for your home. But if you understand how to use this information correctly to choose the ideal system, you’ll be one step closer to having soft water at home. Take your time to compare the best water softener brands on the market, and choose the best.

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