How to Size a Water Softener in 5 Simple Steps – Need Help?

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You know how one-size-fits-all clothing fits few people well? Water softeners are a bit like that. A water softener that’s not the proper fit for your home will still work, but not nearly as well as it could if you purchase the correct size.

The size is determined by how many “hardness grains” a water softener is capable of removing before a regeneration cycle is needed. Neither too many nor too few cycles is a good thing. Too low of a grain rating will rapidly exhaust the resin bed, resulting in lowered water pressure and more frequent maintenance. The water softener will also wear out more quickly. On the flip side, a water softener that’s larger than needed will regenerate too infrequently, which will harm the resin bed over time. Plus a larger water softener costs more.

Don’t worry, Goldilocks! With a few quick calculations, you can easily figure out which water softener will fit your home’s needs just right.

What Size Water Softener Do I Need? – Calculating the Ideal Water Softener Size in 5 Simple Steps

If all of this sounds like gibberish, it’s not as complicated as you think. Water softeners work by removing hardness minerals, primarily calcium and magnesium, from your water. The more minerals the water contains, the larger a water softener you need. Likewise, if your household uses a lot of water each day, you’ll need a larger softener than someone who lives alone and hardly uses the faucet at all. You can’t choose a water softener based on a total guess, however. There are five steps to take to give you a good idea of what size water softener you should purchase.

iron filters and water softeners

1. Test Your Water

Proper water softener sizing starts by testing your water.

As mentioned above, hardness is defined by the concentrations of minerals in your water. The terms used to describe water hardness include soft, moderately hard, hard, and very hard, and are measured in parts per million, abbreviated as ppm. Sometimes, you’ll also see water hardness measured in “mg/L”, which is the same thing. The labels on water softeners will usually measure levels by “grains per gallon”. To convert from ppm or mg/L to gpg, just divide by 17.12.

The exact figures defining each category vary slightly, but not by much. In general,

  • 60 ppm or less is considered soft water,
  • 61-120 is moderately hard,
  • 121 – 180 is hard,
  • and over 180 is very hard water.

Many people are clued-in to hard water issues by the telltale signs of scale around the bathroom drain and hard water spots on the shower door. When it comes to sizing a water softener, however, guessing how hard your water is isn’t good enough. You need to know the exact hardness measurements before moving on to the next step.

The good news is, testing your water is quick and inexpensive. You can even do it yourself! Tons of test kits are available on Amazon, but you can also send out a sample to be tested at an independent lab if you’d rather rely on a pro. If you’re on city water, you can also call the supplier and ask for a report, or look up a past report online.

Iron levels are another issue entirely, and one that’s a notable issue for homes running on well water. While you’re testing for hardness, test for iron, too. For every 1 ppm of iron, add 4 gpg to your water’s hardness value. If your manganese is high, add on 4 gpg for each ppm of manganese as well.

2. Guess About How Much Water You Use Per Day

The easiest way to calculate your household’s daily water usage is by taking a look at your most recent water bill. Usually, water bills include a figure for your average water usage over a certain period of time, usually a month or a season. Use this figure to determine your average daily water consumption.

Some people, say those who’s water bill is included in their HOA payments, can’t easily find this info. If this is the case for you, it’s okay to estimate. The USGS estimates that each person uses 80-100 gallons of water per day, so all you need to do is multiply this figure by the number of people living in your home. If most of your family members love long, luxurious showers and wash laundry frequently, multiply by 100. If you’re a very water-conscious household, multiply by 80.

If in doubt, guess higher. It’s better to have a slightly higher softening capacity than you need than to struggle with drops in water pressure if your water softener can’t handle your typical usage.

3. Figure Out Your Daily Softening Needs

The next step is easy as pie. To find out how many grains your water softener will need to remove each day, multiply your measured water hardness level by your household’s average daily water usage in gallons. For example:

12 hardness grains per gallon * 240 gallons per day = 2,880 hardness grains per day

Not everyone loves math, but it’s not that hard if you break it down. If you use 240 gallons of water every day and there are 12 grains of hardness in each gallon, your new water softener will need to be able to trap a minimum of 2,880 hardness grains per day.

4. Calculating the Required Grain Capacity


Water softeners trap hardness grains within their resin bed, so it makes sense that eventually the bed can get too full of minerals to trap any more. At this point, a water softener needs to regenerate. During each regeneration cycle, all built up minerals are rinsed out and washed away. Also, the resin is replenished with sodium or potassium required to trap more hardness ions.

On average, water softeners need to be regenerated about once a week. This frequency strikes a happy medium, keeping your softener working efficiently and reducing the amount of wastewater produced. It also limits wear and tear on the most critical components of your water softener, like the delicate resin bed.

To calculate how many water hardness grains need to be removed per week, multiply the daily softening requirement by 7 days. For example:

2,880 hardness grains per day * 7 days = 20,160 grains per week

5. Consider Salt Efficiency of Different Models

The last step is a little more complicated to understand, but we believe in you!

From what we’ve learned above, if you need to remove roughly 20,000 grains per week, a water softener with a 20,000-grain rating could be regenerated once a week and you’d always have a fresh supply of soft water. While that’s true in theory, there’s one additional factor to take into account: salt efficiency.

Also known as brine efficiency, salt efficiency refers to the amount of hardness grains removed per pound of salt. To soften 20,000 grains using a water softener with a 20,000-grain rating, you’d have to fully regenerate the resin bed each time. This requires MUCH more salt than if the resin bed of a larger system, let’s say 30,000-grain, were only partially regenerated.

Technically, the first model could remove 20,000 grains between each regeneration cycle, but it would require using much more salt than if only a partial regeneration were conducted. For example:

Recharging 2/5ths of the softening bed might require only 1/5 the salt. Three-fifths of the salt could recharge the resin bed over 80%.

So remember: The more salt used at a time, the higher the softening capacity, but the lower the salt efficiency. To save money on salt and reduce waste, choose a water softener that can remove more hardness grains per week than you actually need. That way, you can maximize your salt efficiency without ever running out of softened water! Because less salt will enter the waterways, the environment will thank you, too!

Check the Grains Per Pound of Salt Rating

All models are not created equal when it comes to salt efficiency. Every water softener should include a rating that shows how many hardness grains it can remove from water per 1 pound of salt and at the minimum salt dose – the more grains the better! This reflects real-life usage, and you’ll be surprised to see how much the salt efficiency varies from water softener to water softener. Softeners in some states are required to have a certain minimum efficiency level. In California, for example, efficiency must be a minimum of 4000 grains per pound of salt. Meanwhile, water softeners with NSF Standard 44 certification are verified to operate at a minimum efficiency of 3350 grains/pound.

Water Softener Reviews
Do you now know your ideal water softener size? Then you might want to continue with reviews of our favorite water softeners:

Additional Sizing Considerations


A water softener’s grain capacity rating indicates how many hardness grains the model can process before a regeneration cycle is needed. Models with a lower rating need to regenerate more frequently than models with a higher rating. Higher-rated models can remove more minerals because they contain larger resin beds, measured in cubic feet. The only problem is that the higher the volume, the larger the tank size. Before you size up to a water softener with a higher capacity, make sure you have the space for it.

Water Softener Tank Size Chart

ResinTank Size (Diameter * Height)Rating
0.75 ft³8″ * 44″15,000 grains
1.0 ft³9″ * 48″20,000 grains
1.5 ft³10″ * 54″30,000 grains
2.0 ft³12″ * 52″40,000 grains
2.5 ft³13″ * 52″50,000 grains
3.0 ft³14″ * 65″60,000 grains

Don’t Forget Flow Rates

Softening capacity says a lot, but it’s not everything. It’s also crucial to check the flow rate of a potential new water softener. If the rating is too low, the system will struggle to keep up when you need water the most. Think about on weekday mornings when everyone in the house is rushing to get ready for the day. With back-to-back showers, water running in the kitchen, someone brushing their teeth in the bathroom, etc, it’s likely you’ll need to use a lot of water all at once.

Flow rates are measured in gallons per minute, so you’ll want to be sure a water softener has a high enough flow rating to handle your home’s peak water usage. Usually, larger homes with more people need higher flow rates. For a household with multiple bathrooms, the lowest flow rating you should look for is about 12 gpm. For smaller households, about 7 gpm is likely sufficient. Have a large family or frequently host overnight guests? Look for a water softening system that offers 15 gpm at a bare minimum.

If you’d like to get a more exact figure, get an approximate picture of how much water you use during peak consumption periods by adding up elements from the following list. For example, on a busy morning, your family might run two showers, two faucets, and flush the toilet all at the same time, adding up to a total of 10 gpm.

Standard Outlets: Water Use

Outlet TypeWater Usage
Kitchen faucet1.5 – 2.2 gpm
Bathroom tap1.0 gpm
Shower head2.0 – 2.5 gpm
Toilet3.0 gallons per flush
Dishwasher4.0 – 15.0 gallons per load
Washing machine15 – 30+ gallons per load

Choosing a Commercial Water Softening System

Because there are so many factors that help determine the correct size of a water softener needed for commercial purposes, we advise against trying to figure this out yourself. For large, complicated configurations, turn to a local professional. It won’t be inexpensive, but you can rest easy knowing the job will get done right.

And that was our water softener sizing guide. If you still don’t know how big of a water softener you need, let us know and we’ll help you out!

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