What size water softener do I need?

Last updated on: May 1, 2022.

Water softeners are useful household products that turn hard water into soft water. Hard water contains mineral ions such as magnesium and calcium. Telling signs of hard water include residue on appliances, soap scum in sinks, and dry skin after showers.

Untreated hard water can cause long-term damage to your utilities and increase repair costs. Mineral buildup can restrict water flow, reduce pressure and damage your pipes.

Efficient water softeners remove mineral ions from your water to provide soft water. This can improve the quality of your drinking water as well as prevent mineral buildup in household appliances. Dishes, clothes, and your skin will feel softer and cleaner than before. There are several benefits of installing a water softener in your household.

However, there are several water softeners in the market that come in various shapes and sizes. A water softener that is the wrong size for your household can be inefficient and cause more damage than benefits.

Getting a correctly sized water softener that meets your requirements can be intimidating. This guide explores the factors you need to consider when purchasing a water softener. It will help you pick a correctly sized water softener to ensure a steady supply of soft water for your household.

Can a water softener be too big?

It is better to get a water softener that is bigger for your requirements than smaller. However, there are problems that will arise if your water softener is too big for your household.

Water softeners that are too large for your household needs do not regenerate often enough. This can damage the resin beads and lead to bacterial growth in the tank.

Additionally, larger water softeners cost more upfront. It is recommended to get a water softener that can be up to thirty percent larger than your needs to cover high usage periods. Anything larger than this is ultimately detrimental.

Water Softener Sizing Chart: How to calculate the right size for your water softener?

To calculate the size of the water softener you need, there are two important factors to consider. These are the hardness of your water and your daily water consumption. Following this, you may calculate other factors like a daily softening requirement, grain capacity, and salt efficiency. These factors combined will help you decide the correct size of the water softener you need in your household.

Step 1: Water Hardness

You measure water hardness in grains per gallon(gpg), parts per million(ppm), or milligrams per liter(mg/L). You can determine the hardness of your water by purchasing home testing kits. You could also get your water tested by professionals for more reliable results.

It is important to have an exact number that measures your water hardness. Merely guessing this number can lead to improper sizing. Below is the range of numbers you can see to determine water hardness.

The acceptable range of water hardness:

Soft water – 0-60 mg/L or ppm; 0-3gpg

Moderately hard – 61-120 mg/L or ppm; 3-7gpg

Hard – 121-180 mg/L or ppm; 7-10gpg

Very hard – >180 mg/L or ppm; >10gpg

Step 2: Daily Water Consumption

The next step is calculating how much water your household consumes on a daily basis. The most reliable way to do this is to refer to your water bill. It will provide a monthly or quarterly amount of water consumed over a certain timeframe. Use this to calculate your daily water consumption. 

If you do not have access to this information you can use a simple calculation. It is estimated that a single person uses between 80-100 gallons of water per day. 

Multiply the number of people living in your household by 80 to 100. Use 80 if you use water fairly conservatively and 100 if you are lavish in your water consumption. This will give you an estimation of the gallons of water your household uses per day.

For example, if you have 4 people in your household and you multiply that with 100 gallons per person you get 400 gallons of water per day.

Step 3: Daily Softening Requirement

This step is calculating your daily softening requirement. To do this, simply multiply your water hardness by your daily water consumption. For example, your tests show you have water hardness at 10 grains per gallon. From step two, you know that your household consumes 400 gallons of water per day.

Multiplying these numbers gives you 4000 hardness grains per day. This means your new water softener will have to remove 4000 hardness grains per day to meet your requirements.

Step 4: Total Grain Capacity of Water Softeners

Water softeners have a regeneration cycle. This means that they can only remove a certain amount of hardness grains before needing to regenerate. At some point, all the resin beads become saturated and cannot bind any more mineral ions.

Regeneration involves washing out the accumulated minerals and recharging the resin bed with sodium or potassium. 

Water softeners have different regeneration cycles ranging from daily to once a week. To calculate total grain capacity, multiply your daily softening requirement by the number of days in the regeneration cycle.

For example, if a water softener has a 6-day regeneration cycle. Using the statistics used in previous steps, you multiply 4000 by 6.  This means 24,000 grains is your total grain capacity.

Step 5: Salt Efficiency

It is important to also consider salt efficiency. Regenerating a water softener’s resin bed to 100% requires a disproportionately high amount of salt. Partial regeneration thus becomes a lot more efficient.

For example, around 12 pounds of salt are required to fully regenerate a 30,000-grain system. The same model can use less than 2 pounds to regenerate 10,000 grains.

Recharging only 40% of the softening bed requires only one-fifth of the salt amount. Three-fifths of the salt amount can recharge up to 85%. If you require a water softener that requires the removal of 24000 grains per week as calculated above, it is recommended to choose higher grain capacity water softeners. 

This will save a lot of money and use less salt in the long run. Servicing your system will be easier and there will be less wear and tear on your water softener.

Letting your water softener regenerate to 100% will make it exhaust faster. It is recommended to choose a water softener that is around 30% larger than your requirements.

This will ensure that your water softener isn’t too big, which can lead to regeneration not occurring often enough. This in turn will damage resin beads and increase repair costs.

Therefore the best-sized water softener as calculated in previous steps in a 32000-grain capacity filter. This size is the best choice for the household in this example. 

Step 6: Water Flow Rates

After you’ve determined the appropriate size for your water softener, it is also important to consider water flow rates. If your water softener cannot deliver enough soft water during peak usage, hard water may leak through and water pressure will reduce.

This is particularly important when there are multiple taps running, for example in the morning when the entire family is getting ready for their day.

Water flow is measured in gallons per minute(GPM). The more people live in your house, the more flow rate you need.

Single households can use around 5 GPM while bigger families should ensure that they get systems providing at least 15 GPM.

How do you size a commercial water softener?

The flow rate or gallons per minute are important considerations in sizing commercial water softeners. You want a water softener that keeps up with consumption and regenerates often.

There are several other considerations such as water temperature, water pressure, capacity per cubic foot of each softener tank, and how much space is available. This is a much more complicated process than sizing a water softener for home use.

Therefore, it is highly recommended that you contact a specialist who can factor in all the elements and correctly size a commercial water softener for your establishment. 


Water softeners are useful household products that can offer several benefits in treating hard water. The soft water that these products provide has several benefits from more efficient cleaning to healthier drinking water.

In order to get the most out of a water softener, and enjoy good water quality, it is important to get one that meets the requirements of your household.

Incorrectly sizing your water softener can compromise the benefits they offer and lead to long-term damage and expenses. Calculating the size you need is as simple as acquiring information about your household and its requirements.

Frequently Asked Questions:

1. At what hardness is a water softener needed?

Generally, water is considered hard if it tests for over 100 ppm or mg/L and over 7 gpg.

You can determine how hard your water is by testing it with a DIY kit or by hiring professionals. Your water should measure between 0-60 ppm or mg/L and between 0-3 gpg to be considered soft water that is safe for your household. 

What size water softener do you need for a family of 5?

The size of the water softener you need for a family of 5 is determined by how hard your water is and how much water is used daily. You may follow the steps in the sizing guide to get an exact requirement.

Generally, if your water measures 10 grains per gallon and each member uses 100 gallons of water per day you need 5000 grains softened daily. Multiply that by each day of the week and you get 35000 total grain capacity.

It is advisable to get a softener that is around 30% larger than your requirements.

In this case, you will need a water softener with a 45000 total grain capacity. If your water is not that hard or you use less water per day, this number can be reduced.

Alternatively, if your water is harder and you consume more water, this number will increase.

How many cubic feet is a 48000-grain water softener?

A 48000-grain water softener will measure 1.5 cubic feet.

How do you convert grain gallons to PPM?

1 grain per gallon(gpg) is 17.1 parts per million(ppm). You can use this information to convert between gpg and ppm. For example, 10 gpg is 171 ppm.

About The Author

Our Web Producer

Judith— a passionate water treatment specialist — is a waste water management enthusiast, clean drinking water advocate, and someone with deep personal experience and knowledge about various water equipments. Her work was mentioned in countless notable water associations. Previously she was an editor at Water Alliance.