What size water softener do I need?

If your home gets hard water, a water softener is the go-to solution.

As water travels through soft rock like chalk, gypsum, or limestone, it absorbs magnesium, calcium, and other minerals, creating hard water.

Hard water causes a bunch of frustrating results: white spots on utensils; misty shower doors; cloudy glasses, and deposits in pipes and water heaters. It can also dry out your skin and hair.

Hard water is super common in the US, which is why so many people head online to research the best water softeners. But once you’ve chosen a system, how do you find out what size water softener you need?

In this article, we’ll explain how to figure out the correct size water softener for your household in four simple steps.

Salt pellets for the water softener

What is a Water Softener?

A water softener removes the hard mineral ions (usually magnesium and calcium) from water by attracting and swapping them with a small amount of salt.

The science behind this process is called ion exchange. Hard mineral ions like magnesium and calcium have an opposing charge to pure salts like sodium and potassium.

When hard water enters a softener tank, it flows through a resin bed saturated with salt ions. Here, an bonding and exchange process occurs, where calcium and magnesium ions are pulled from the water and sodium or potassium ions released.

Why Size Matters

Choosing a water softener that’s reliable and good value for money is important. But selecting the right size model also matters, because you want the softener to run efficiently, while only refilling it with new salt as infrequently as possible.

  • Buying a softener with a capacity that’s too small will mean that you’re constantly refilling salt and dealing with frequent down periods while the system regenerates.
  • Buying a softener that is too big for your needs will mean shelling out more cash than is required, and may cause clogging (in the form of salt bridges) in your brine tank due to under use.

How to Choose the Right Water Softener in 4 Steps

1. Determine your water hardness

Hard water contains a high concentration of calcium and magnesium. To determine how hard your water is, it’s best to purchase a hard water test kit from a home improvement store.

If you’re on city water, you can also contact your local water supplier for hardness information, as they may keep data records.

Most water hardness measurements are in mg/L (milligrams per Litre). To help choose a water softener size, you’ll need to convert mg/L into GPG (grains per gallon).

A “grain” of water hardness is equivalent to 1/7000th of a pound. Divide mg/L by 17.1 to convert it to GPG.

A mild water hardness level, in the 1-3 grain per gallon range, means there is some, but fairly little dissolved calcium and magnesium in your water.

Water that is considered very hard has 7-10 grains per gallon.

2. Know your average household water consumption

You’ll also need to know roughly how much water your household uses on an average day.

Average domestic water use is in the US is around 75 gallons per day, per person. But if your family uses more water (big laundry loads, long showers), water volume can quickly rack up to 100 gallons per person.

So if you have a family of 4 and everyone uses the average amount – your house’s water volume is likely to be upwards of 300 gallons per day.

3. Calculate Your Daily Softening Requirement

To determine the right water softener size, all you need to do is multiply your daily water usage by your water hardness:

  • Multiply the number of people in your family by 75 gallons per day. This answer is your approximate daily water use.
  • Multiply your water hardness GPG by the daily water use. This answer is your daily softening requirement.

Once you know this number, you can match it up with a water softener resin that has a similar grain capacity.

Let’s do a full calculation together: If we’re living in a 4 personal household and we each use roughly 80 gallons of water per day, we get to 320 gallons of total daily water use.

If our water is quite hard, around 8 grains per gallon, then we would multiply 320 x 8 to get 2,560 grains as our daily softening requirement.

Important to note: You need to adjust for iron if it’s also present in your water supply.

4. Pick the right regeneration frequency

The final step is to compare your daily softening requirement with a softener’s regeneration period.

Most softeners will function for multiple days between regenerations. They either regenerate on a set timer or contain a sensor to auto-manage regeneration.

Generally, water softeners have enough capacity to last 3-7 days between regenerations. Check your chosen product to find out how quickly it regenerates, then multiply this number by your daily softening requirement.

Example: If we know our softener needs to regenerate every 7 days, we can multiply our daily softening requirement by 7. 2,560 x 7 = 17,920. This is our final number, our required capacity in between regenerations.

4 or 5-person families will typically need a 24,000 or 32,000-grain capacity water softener, depending on the specifics of their situation.

Softeners that auto-modulate regeneration can use their salt more efficiently than softeners that regenerate on a set timer. Scroll down for more on the nuances of regeneration.

Extra info!

Since we don’t want to have to refill our softeners with salt every day, but we still want to ensure that they are doing their jobs efficiently, most manufacturers design softeners with about a week’s regeneration cycle in mind.

What is a regeneration cycle?

In essence, it’s the term used to describe the flushing out of the collected minerals that it has extracted from the hard water that has passed through the softener.

At a certain point, the softener has trapped all the hardness minerals it can handle and becomes saturated. At that time, it needs to be flushed out and cleaned such that it can continue to soften new water.

Why does regeneration period matter?

Knowing a softener’s regeneration period matters for water softener sizing because it gives us a timeline to plan around.

If we have a water softener that needs to regenerate every 7 days, then we know we need to multiply our daily grain requirement by 7. The end result is that we need a softener capable of softening about 28,000 grains between regenerations.

Many more expensive water softeners will allow you to program your own regeneration period, or pick from a number of pre-set cycles. This gives you great flexibility when both using and choosing your system.

In addition to household water softening needs, a note should also be made regarding water softener efficiency. Efficiency speaks to how much salt is required to run a water softener at its maximum capacity.

Efficiency is significant because oftentimes a lot of salt is needed to run a softener at its full capacity, and so you can potentially benefit by purchasing a softener that has the ability to filter out more grains than you require but buying less salt.

Accordingly, this is equivalent to putting up more money upfront for a larger softener, knowing that you will be able to save on salt costs down the line. Over the entire lifespan of a water softener, buying a higher salt efficiency softener will save you time and money.

For example, let’s say that your water softening requirements are around 21,000 grains per week. You could easily buy a softener that filters in the 24,000-grain level. However, it will take a large amount of salt – in the neighborhood of 25+ pounds – to fully regenerate the machine such that it can filter the full 24,000 grains. Similarly, a 32,000-grain capacity machine takes about 35+ pounds of salt every time it regenerates to get the full-grain capacity.

However, using less salt in a larger machine, say about 6 pounds of salt in a 32,000-grain machine, will get you about 20,000 grains of softening. This is because larger capacity machines have more resin, and thus even when they operate with less salt, can still provide a fairly high degree of softening.

For the majority of brands, a 32,000-grain water softener will have about 1 cubic foot of softener resin. A 48,000-grain system usually has about 1.5 cubic feet, while a 64,000-grain system will have about 2 cubic feet. But remember, this assumes the lowest salt efficiency setting, meaning the highest amount of salt is used, costing you more in the long run.

Running on the highest salt efficiency (that is, using the least amount of salt possible), a softener with 1 cubic foot of resin will have about a 20,000-grain capacity, a softener with 1.5 cubic feet will have about a 30,000-grain capacity, and 2 cubic feet of resin will yield approximately 40,000 grains.

So before you make a decision on sizing your water softener based purely on the water requirement, be sure to consider your long-term salt costs.

Softener Resin Size Grains Capacity
0.75 Cubic Feet 15,000
1.0 Cubic Feet 20,000
1.5 Cubic Feet 30,000
2.0 Cubic Feet 40,000
3.0 Cubic Feet 60,000
4.0 Cubic Feet 80,000

Sizing Your Water Softener: The Bottom Line

In a nutshell, you need to know three things to find the right size water softener for your home:

1. Your water hardness

2. Your water consumption

3. The regeneration period of your chosen softener.

With these three pieces of information, you should be able to find a system with the perfect capacity for your home. If you’re a part of a 4 or 5 -person family, that probably means a 24,000 or 32,000-grain capacity water softener.