Water Softeners Size Calculator: How Big Should It Be? (3 Size Charts)

“We are a 4-member family, have a 2,000 sq ft house in North Dakota. What size water softener do I need for my home?”

This is a standard water softener size question every household has to answer. To help our everybody who doesn’t want to undersize or oversize their water softener, we have created a Water Softener Size Calculator that determines how many grain water softener you need.

On top of that, we also created 3 water softener size charts (1st for “Moderately Hard” water, 2nd for “Hard” water, and 3rd for “Very Hard” water households). This should, in the end, answer if you need a 24,000-grain, 30,000-grain, 36,000-grain, 48,000-grain water softener, and so on.

Note: If you don’t get a good answer, you are always welcome to use the comment section below, give us a few numbers, and we can do some math for you.

To adequately figure out how big a water softener you need, we have to consider 3 key factors, namely:

  1. Water usage (in terms of gallons/month). The best way to get this info is just to check your last month’s water bill. Every water bill will have a line denoting how many gallons of water you used in a month.
  2. Water hardness (in terms of GPG). For sizing a water softener, we need to know how hard our water actually is. The harder the water, the more grain water softener you will need. You can convert water hardness PPM to GPG here, and dH (dGH) to GPG here.
  3. Iron content. If you have a significant iron concentration (Fe2+ ions), we need to account for that as well. For every 1 PPM of iron ions, we have to add 5 GPG to water hardness.

Once you have all these 3 data points, you just insert them in the following water softener size calculator, and get the size of water softener you will need. You can read all about how to calculate the size of water softener (the math) here.

Below the calculator, we also present 3 water softener size charts for households with “Moderately Hard” water (1st chart), “Hard Water” (2nd chart), and “Very Hard” water (3rd chart), in accordance with the water hardness scale available here.


Alright, let’s solve one example just to see how this calculator works:

Say you have a big 5-member family that uses 13,500 gallons of water per month. You have measured you have 95 PPM water hardness. Converting PPM to GPG with this calculator, you see that 95 PPM is equal to 5.55 GPG. Water analysis also showed you have 0.48 PPM iron content. How big water softener does this household need?

Simple. Just slide the 1st water usage slider to ‘13500’, 2nd GPG slider to ‘5.55’, and 3rd iron content to ‘0.48’. Here is a screenshot of how to do all that (with results):

water softener size calculator example

You can immediately see that this household has:

  • “Moderately Hard” Water. This means that the water hardness is within the 3.51 GPG to 7.01 GPG (or within the 61 PPM to 120 PPM) range.
  • 33,385-Grain Capacity Water Softener. This is the optimum water softener size. In practice, you would go with a 34,000-grain water softener in this case.

Alright, based on water usage, water hardness, and iron content, you may need anywhere from 4,000-grain to over 100,000-grain water softener. Let’s have a look at how to estimate the size of water softener with a manual calculation (+ formula):

What Size Water Softener Do I Need? (Grain Capacity Sizing Formula)

As we have described in-depth in our “How To Size A Water Softener” article here, we need to account for these 4 factors when sizing a water softener:

  1. Water Usage.
  2. Water Hardness.
  3. Iron Content.
  4. 75% Efficiency/Brine Salt Usability.
how big should a water softener be
A rule of thumb is to regenerate the water softener with the salt from the brine tank (on the photo) once per week.

On top of that, we also need to account for once-per-week regeneration frequency. Based on all these factors, we can write the water softener sizing formula like this:

Water Softener Size (Grains) = (Water Hardness (GPG) + Iron Content (PPM) × 5) × Monthly Water Usage (Gallons) / (0.75 × 4.3)

This seems like a snake of an equation, but let’s solve one example with it to demonstrate it’s actually quite easy to use (obviously, the calculator and the following 3 sizing charts are much easier to use):

Say you have a 1,500 sq ft home. You use 11,500 gallons of water per month. Water analysis has shown that the water hardness in your home is 9 GPG, and you also have 0.25 PPM of iron ions (Fe2+). What grain water softener do you need here?

Let’s insert all of this data into the equation above like this:

Water Softener Size (Grains) = (9 GPG + 0.25 PPM × 5) × 11,500 Gallons/Month / (0.75 × 4.3) = 36,550 Grains

You can see that we need a water softener with about 36,550 grains. In this case, we would opt for a 36,000-grain or 37,000-grain unit.

Now, this is just one example of a household with “Hard” water (according to water hardness categorization). To help every possible household out, we have created 3 water softener sizing charts that will help you out (without iron content in their water):

  • 1st chart is for households with “Moderately Hard” water (3.5 to 7 GPG water hardness). Here, you see that you need anywhere from 4,000-grain to 40,000-grain water softener capacities.
  • 2nd chart is for households with “Hard” water (7.5 to 10.5 GPG water hardness). For hard water, you will need anywhere from 10,000-grain to 60,000-grain water softener.
  • 3rd chart is for households with “Very Hard” water (12 GPG and more). Here, the water softener capacity can reach over 100,000 grains.

Let’s start with the 1st “Moderately Hard” water sizing chart and then proceed to charts with the highest water hardness:

Water Softener Size Chart For “Moderately Hard” Water (1st Chart)

“Moderately Hard” Water: 3.5 GPG 4 GPG 5 GPG 6 GPG 7 GPG
4,000 Gallons/Month 4,000-Grain 5,000-Grain 6,000-Grain 8,000-Grain 10,000-Grain
6,000 Gallons/Month 6,000-Grain 8,000-Grain 10,000-Grain 12,000-Grain 14,000-Grain
8,000 Gallons/Month 8,000-Grain 10,000-Grain 12,000-Grain 14,000-Grain 18,000-Grain
10,000 Gallons/Month 10,000-Grain 12,000-Grain 16,000-Grain 18,000-Grain 22,000-Grain
12,000 Gallons/Month 14,000-Grain 16,000-Grain 18,000-Grain 22,000-Grain 26,000-Grain
14,000 Gallons/Month 16,000-Grain 18,000-Grain 22,000-Grain 27,000-Grain 30,000-Grain
16,000 Gallons/Month 18,000-Grain 20,000-Grain 24,000-Grain 30,000-Grain 35,000-Grain
18,000 Gallons/Month 20,000-Grain 22,000-Grain 28,000-Grain 34,000-Grain 40,000-Grain

You can see that many smaller households (1 member, 2 member) with up to about 6 GPG water hardness need a very small water softener (up to about 20,000 grain capacity). Many homeowners with moderately hard water tend to oversize their water softeners, so be careful here; you don’t need the big 48,000-grain units to softer water (overkill).

Bigger 5-member, 6-member, 7-member households with moderately hard water that use more than 15,000 gallons of water per month will need bigger water softeners. Specifically, these households may need up to 40,000 grain capacity water softeners.

Let’s look at households who have “Hard” water:

Water Softener Size Chart For “Hard” Water (2nd Chart)

“Hard” Water: 7.5 GPG 8 GPG 9 GPG 10 GPG 10.5 GPG
4,000 Gallons/Month 10,000-Grain 10,000-Grain 12,000-Grain 12,000-Grain 14,000-Grain
6,000 Gallons/Month 14,000-Grain 16,000-Grain 16,000-Grain 18,000-Grain 20,000-Grain
8,000 Gallons/Month 18,000-Grain 20,000-Grain 24,000-Grain 24,000-Grain 27,000-Grain
10,000 Gallons/Month 24,000-Grain 25,000-Grain 27,000-Grain 30,000-Grain 32,000-Grain
12,000 Gallons/Month 27,000-Grain 30,000-Grain 34,000-Grain 37,000-Grain 40,000-Grain
14,000 Gallons/Month 34,000-Grain 35,000-Grain 40,000-Grain 44,000-Grain 45,000-Grain
16,000 Gallons/Month 37,000-Grain 40,000-Grain 45,000-Grain 50,000-Grain 52,000-Grain
18,000 Gallons/Month 42,000-Grain 45,000-Grain 50,000-Grain 56,000-Grain 60,000-Grain

The harder the water, the more grain capacity water softeners we need. If you check the 10 GPG water hardness column, you can see that big households that use a lot of water (16,000 gallons/month or more) will need a 50,000-grain water softener or larger.

If, on the other hand, you have a small household and don’t use all that much water, you may need below 30,000 grain water softeners.

Water Softener Size Chart For “Very Hard” Water (3rd Chart)

“Very Hard” Water: 12 GPG 14 GPG 16 GPG 18 GPG 20 GPG
4,000 Gallons/Month 14,000-Grain 18,000-Grain 20,000-Grain 22,000-Grain 24,000-Grain
6,000 Gallons/Month 22,000-Grain 27,000-Grain 30,000-Grain 34,000-Grain 37,000-Grain
8,000 Gallons/Month 30,000-Grain 35,000-Grain 40,000-Grain 45,000-Grain 50,000-Grain
10,000 Gallons/Month 37,000-Grain 44,000-Grain 50,000-Grain 56,000-Grain 60,000-Grain
12,000 Gallons/Month 45,000-Grain 52,000-Grain 60,000-Grain 67,000-Grain 75,000-Grain
14,000 Gallons/Month 52,000-Grain 60,000-Grain 70,000-Grain 78,000-Grain 85,000-Grain
16,000 Gallons/Month 60,000-Grain 70,000-Grain 80,000-Grain 90,000-Grain 100,000-Grain
18,000 Gallons/Month 68,000-Grain 80,000-Grain 90,000-Grain 100,000-Grain 112,000-Grain

Households with “Very Hard” water will need the biggest water softeners. These homes can have up to 20 GPG water hardness. How big exactly?

Well, you can see that 30,000-grain units are mostly undersized here. If you have both very high water hardness and use a lot of water, you might be looking at those big commercial 100,000-grain water softeners.

All in all, we hope that the calculator, explanation with the formula, and these 3 water softener size charts will help you estimate how big a water softener you need. If you need our help, you can give us a few numbers in the comment section below, and we will help you with the calculations and estimations.

2 thoughts on “Water Softeners Size Calculator: How Big Should It Be? (3 Size Charts)”

  1. We are a household of 2
    Water is 17 grains of hardness
    House is 1200 square feet 2 bathrooms
    One shower one shower/ tub
    What size softener do you recommend??
    Thank you

    • Hi Sandra, alright, we need 2 pieces of data: water hardness (which we have; 17 GPG, very hard water), and water usage (which we don’t have). A 1200 sq ft household with 2 bathrooms (2-3 member family) will roughly use anywhere from 5,000 to 10,000 gallons/month. Based on this, we are looking at the 26,441-grain to 52,881-grain water softener range.

      This is a very rough estimate. If you have info about how much water you use per month (gallons/month), we can make a better estimation. Usually, you just check your last month’s water bill, and you will see how much water you used last month.


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