What Size Water Softener For Family Of 4? (Calculator + Chart)

You have a family of 4, and you want to get a water softener. The first question that you need to answer here is what size water softener you need for a family of 4. Will a 24,000-grain unit be enough? Do you need a 36,000-grain unit, or even bigger?

Obviously, the water softener is there to protect your piping, washing machine, and other expensive appliances. But you don’t want to get one that’s too small to do the job, nor do you want an oversized one due to needless extra costs and regen cycle problems.

To help you out figuring how big a water softener you need for a 4-family home, we have prepared the following key resources that will help to answer just that, namely:

  1. Family Of 4 Water Softener Size Calculator. Here just insert monthly water usage (gallons/month), measured water hardness (in GPG or Grains Per Gallon), and potential iron content (in PPM or Parts Per Million). The calculator will give you a good idea on what size water softener your family needs.
  2. Two Examples. We looked at two 4-member families and calculated water softener size they need.
  3. Water Softener Size Chart For Family Of 4. We charted how many grain water softener families of 4 need by varying water usage from 4,000 gallons/month to 18,000 gallons/month, and water hardness from 6 GPG to 16 GPG. All the results – water softener capacities – are summarized in a neat colored chart.

We need 3 data points in order to determine water softener size adequately: monthly water usage (gallons/month), water hardness (GPG), and potential iron concentration in water (PPM). Once you have that (we also explain how to get the data further on), you can just insert the data in this calculator, and get the result immediately:


Let’s solve 1st example to show how this calculator works:

Meet the Robinsons. They have a 1,500 sq ft home, dad, mom, and 2 kids. Checking the monthly water bill, they see that they used 7,600 gallons of water in the past month. Dad used a TDS meter to check how hard their water is. He determined that they have 12 GPG water hardness. On top of that, he also measured 0.50 PPM iron content. What size water softener do they need?

water usage for 4 member household from utility bill
We can get the monthly water usage from utility bill or water bill (depends on the state).

Simple. We have all the data we need to insert them into the calculator. We slide the 1st water usage slider to ‘7,600’, the 2nd water hardness slider to ’12’, and the 3rd iron content slide to ‘0.50’. Here is the result we get:

water softener size for a family of 4 with hard water 12 gpg

We can see right away that the Robinsons need a water softener with a 34,280-grain capacity. The closest capacities you will find on the market are 30,000-grain and 36,000-grain units. In this case, the Robinsons should opt for a 36,000-grain water softener.

Note: We have also created a similar calculator for a family of 5. You can check it in our article titled “What Size Water Softener For Family Of 5” here.

Let’s have a look at the 2nd example. This time we will look at the math of how to size a water softener for a family of 4:

How Many Grain Water Softener Does An Average Family Of 4 Need? (Math)

As we have seen, we need to account for 3 factors when determining the size of any water softener (water usage, water hardness, iron content). We can use this water softener size formula to figure out how many grain unit we need for any family size:

Water Softener Size (Grains) = (Water Hardness (GPG) + Iron Content (PPM) × 5) × Monthly Water Usage (Gallons/Month) × 0.2333 / 0.75

Now, let’s look at the 2nd example to see how you can calculate the water softener size manually as well.

Say that we have an average 4 member household. Each person uses, on average, 83 gallons of water per day, which comes to 9,960 gallons per month. They have very hard water that is eroding their piping. The measured water hardness is 250 PPM. Luckily, they have 0 PPM of iron concentration in their water.

The first thing we need to do here is to convert 250 PPM water hardness to GPG. Using this PPM to GPG calculator, we see that 250 PPM is equal to 14.60 GPG. Now we have all we need. Let’s insert these numbers in that ugly equation above like this:

Water Softener Size (Grains) = (14.60 GPG + 0 PPM × 5) × 9,960 Gallons/Month × 0.2333 / 0.75 = 45,234 Grains

We see that this average 4-member family with very hard water needs a water softener with about 45,234-grain capacity. The closest widely available water softener size is 46,000-grain unit; this is the right capacity for this family.

Alright, now that we have a good grip on how to determine how big a water softener we need for a family of 4, let’s construct a chart that will tell us how many grain units we need depending on our water usage and water hardness:

Water Softener Size Chart For Family Of 4

This chart tells you the grain capacity of a water softener if you use very little water (4,000 gallons/month) or boatloads of water (16,000 gallons/month). We are also looking at water hardness from moderately hard water (6 GPG) to very very hard water (18 GPG). We presume no iron content.

Here is the full chart:

4 Member Family: 6 GPG 8 GPG 10 GPG 12 GPG 14 GPG 16 GPG 18 GPG
4,000 Gallons/Month 8,000-Grain 10,000-Grain 14,000-Grain 16,000-Grain 18,000-Grain 20,000-Grain 24,000-Grain
6,000 Gallons/Month 12,000-Grain 16,000-Grain 20,000-Grain 24,000-Grain 27,000-Grain 30,000-Grain 36,000-Grain
8,000 Gallons/Month 16,000-Grain 20,000-Grain 24,000-Grain 30,000-Grain 36,000-Grain 40,000-Grain 46,000-Grain
10,000 Gallons/Month 18,000-Grain 24,000-Grain 30,000-Grain 36,000-Grain 44,000-Grain 50,000-Grain 56,000-Grain
12,000 Gallons/Month 24,000-Grain 30,000-Grain 36,000-Grain 44,000-Grain 54,000-Grain 60,000-Grain 68,000-Grain
14,000 Gallons/Month 24,000-Grain 36,000-Grain 44,000-Grain 54,000-Grain 60,000-Grain 68,000-Grain 78,000-Grain
16,000 Gallons/Month 30,000-Grain 40,000-Grain 50,000-Grain 60,000-Grain 70,000-Grain 80,000-Grain 90,000-Grain
18,000 Gallons/Month 36,000-Grain 44,000-Grain 54,000-Grain 68,000-Grain 78,000-Grain 90,000-Grain 100,000-Grain

We can see that a family of 4 needs anywhere from a mere 8,000-grain to 100,000-grain water softener. This is quite a big range; of course, the precise grain capacity depends on monthly water usage and water hardness.

Most 4-member household will need a 24,000-grain, 36,000-grain, and 44,000-grain units. If you have high water usage (over 10,000 gallons/month) and very hard water (over 10 GPG), you might a 54,000-grain, 60,000-grain, or even larger water softeners.

We hope that this illustrates well the size of water softener needed for a family of 4. If you need any help or would like for us to do some calculations for you guys, you can use the comment section below, give us a few numbers, and we can help you out.

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