What Size Water Softener Do I Need? (How to Size a System)

When it comes to buying a water softener for your home, size matters.

Correctly sizing a water softener will help you to minimize salt and water usage – therefore cutting costs – as you tackle hard water at home.

If you’re asking: “What size water softener do I need?”, or, “How many grains per gallon water softener do I need?” this guide will provide you with all the information you’re looking for.

📌 Key Takeaways:

  • To correctly size a water softener, you’ll need to know your water hardness and water consumption.
  • Multiply your average daily water consumption (in gallons) by your water hardness (in GPG), then multiply this figure by 7 to calculate your required water softener grains capacity.
  • Sizing a water softener correctly is essential to ensure your softener can produce enough soft water for your household and only regenerate when necessary.

Note: This article discusses how to size conventional ion exchange water softeners, NOT salt-free water softeners.

📏 How to Size a Water Softener

To properly calculate the size of a water softener, you’ll need to know:

  • Your water hardness
  • Your average daily water usage

👉 Size your water softener in just a few clicks with our Quiz

Determine Your Water Hardness

Water hardness is measured in grains per gallon (GPG), or parts per million (PPM), which is equal to milligrams per liter (mg/L).

You can find out what your water hardness is by using a testing kit.

HardnessGrains per Gallon (GPG)Parts per Million (PPM) & mg/L
Soft<1 0 – 17
Slightly Hard1.5 – 517 – 60
Moderately Hard3.5 – 7 60 – 120
Hard7 – 10120 – 180
Very Hard>10>180
water hardness scale

The higher your water hardness (the amount of dissolved calcium carbonate and magnesium ions in the water), the harder your water softener will need to work to soften your water. Excess iron in your water will also require more salt per gallon of water softened. 

If you have high water hardness and/or iron, look at a softener with a bigger grain capacity that holds enough resin beads to properly soften your water without getting exhausted.

If your water doesn’t have high levels of hardness, you can opt for a softener with a smaller grain capacity for your home.

Calculate Your Water Consumption

It’s also important to know how much water you use per day, on average.

This means all the water you use, not only your drinking water usage.

Water usage is affected by:

  • The number of people in your household
  • The number of appliances in your home
  • How often these appliances are used & their efficiency

If you’re on a municipal or city water supply, look at your water bill to get an idea of your monthly water consumption. You can use this information to calculate an average of your water use per day.

The higher the volume of water you use per day, the bigger capacity water softener you’ll need.

If your water use is lower, you can get a softener with a smaller capacity.

If you don’t have access to your water bill or you’re on well water, you can calculate an average daily water consumption by multiplying the number of people in your household by 75.

For instance, you have a family of 3, you’ll need around 3 x 75 gallons (per person), or roughly 225 gallons of soft water per day.

How to Calculate Your Water Softening Requirements

To size water softener for your own household, use the following formula:

Average Daily Water Consumption x Water Hardness (grains per gallon) x 7 = Water Softener Capacity Requirement

Let’s use an example calculation with 10 grains per gallon of water hardness and 225 gallons of water:

225 X 10 = 2,250 grains of daily water hardness

Most ion exchange softeners are designed to regenerate about once a week. So, the next step is to multiply your daily water softening requirement by 7:

2,250 x 7 = 15,750

Most water softeners are available in the following sizes:

  • 24,000 grains
  • 32,000 grains
  • 48,000 grains
  • 64,000 grains

So, in this example, you’d round up to a softener with a 24,000 grain capacity.

installing the springwell WS1 whole house well water iron filtration system

🤔 What To Consider When Sizing A Water Softener

Capacity and efficiency are both big things to think about when deciding on which water softener is for you.

Water Softener Capacity

What does “grain capacity” mean?

A water softener’s capacity is a measure of the amount of hardness minerals it can eliminate from your water before regeneration is needed.

A single grain of hardness measures up to approximately 1/7000th of a pound of dissolved hardness minerals.

So, a water softener system that has a 24,000 grain capacity can remove around 24,000 grains of hardness before regeneration.

You can use the calculation above to work out roughly how many grains of water hardness you use per week, and you can then match up your softening requirements with a water softener of the best softening capacity.

Water Softener Efficiency

A water softener’s efficiency is calculated by comparing the amount of hardness removed from the water with the amount of salt and water needed for the regeneration process.

There are many things that can affect the efficiency of a water softener, including:

  • The salt dosage. Salt dosage determines the softening capacity of the resin bed. To some extent, increasing the salt dosage improves the exchange capacity. However, you will eventually reach a point where increasing the salt dosage will only minimally increase the exchange capacity. So, higher salt dosages are less efficient than low salt dosages.
  • The water softener’s regeneration mode. Using a water softener that regenerates based on a timer, rather than your water usage, will likely cause the softener to regenerate when it doesn’t need to, wasting salt in the resin tank.

The efficiency of a water softener dictates how much salt you need to buy, use, and release into the environment.

Be sure to consider the salt efficiency of a water softener when you’re selecting the size. High efficiency water softeners use the least amount of salt as possible, but also never run out of soft water.

This will reduce your maintenance requirements and keep your costs as low as possible throughout the water softener’s lifespan.

Related Content: Read our 2023 water softener system cost guide

low salt in softener brine tank

Common Water Softener Sizes

What size water softener do you need – and what sizes are even available?

The most common system size is 32,000 grains, and most families do find that this is the ideal size for their softening needs, though you may opt for the next size up if your family members are a fan of long baths and showers.

The most common water softener sizes are as follows:

  • 24,000 grains
  • 32,000 grains
  • 48,000 grains
  • 64,000 grains

A 64,000 grain softener is typically for commercial use, though some large households do use them in their homes if their gallons per day of water consumption is particularly high.

You can also buy water softeners in two different styles: single-tank and dual-tank softeners.

The only real difference between the two is that single-tank softeners provide soft water on demand, while dual-tank softeners provide you with soft water whenever you need it. When one resin tank performs a regeneration cycle, the water softener simply uses the other resin tank.

🧐 Why Is Water Softener Size So Important?

Choosing a softener with a suitable grain capacity is essential to ensure the system can produce soft water consistently without running out of salt or regenerating too frequently. With the correctly sized, efficient system, you’ll reduce how much salt and water is used, helping you to save money in the long run.

Problems With An Undersized Water Softener

An undersized water softening system might struggle to provide enough soft water that your home needs. So, if you tried to use too much water at once, you’d end up with hard water as the unit would be bypassed. This is far from ideal since the whole point of installing a softener is to prevent scale formation entirely.

Additionally, an undersized water softener will need to regenerate too frequently because the resin’s softening capacity will be maxed out very quickly. Too-frequent regenerations will shorten the lifespan of the resin beads and increase your water expense.

demand initiated water softener regeneration setup

Problems With An Oversized Water Softener

If you buy an oversized water softener, you’ll end up paying more money upfront unnecessarily because you’ll require less salt to soften your water than the system is designed to use.

Plus, the softener may regenerate so infrequently that the resin becomes damaged by fouling and bacteria buildup. The system’s water pressure might also be too high for your home.

🧠 How to Size Water Softener: FAQ

How much hardness is ideal?

After installing a softener, your water hardness level should be 0-3 GPG (grains per gallon). As long as you accurately set your total hardness value in your water softener, it should achieve this optimal range.

What’s a good water softener size for a family of four?

A 32,000-grain ion exchange softener is best suited to a family of four. If your water usage is higher than average or you have extremely hard water, consider a 48,000-grain water softener instead.

Can you install a water softener yourself?

Yes, you can install a softening system yourself – as long as you’re fond of DIY. You’ll need to cut into your pipes and potentially do some soldering. If you’re not a confident DIY-er, you may want to hire a plumber.

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